repair xt250 yamaha 1980- 1983

XT250BK.DOC

MY BOOK ON THE YAMAHA XT250

VERSION 5 DATED June 07.

INDEX

PageINTRODUCTION 3DESCRIPTION. 3YEAR OF MANUFACTURE 5MODEL NUMBERYAMAHA XT 250 G WIRING INFO. 6LOOM MODIFICATIONS 8DIRT BIKE WIRING DIAGRAM 10COMPLETE BIKE WIRING DIAGRAM 11DIAGNOSTICS 12FINDING THAT SPARE PART. 16CONVERTING TO A 12 VOLT SYSTEM. 17MIKUNI CARBURETTOR 18YEARLY MAINTENANCE. 25CLYINDER HEAD 31EXHAUST. 35FRONT FORKS 36OIL LEAKS, HEAD GASKET CHANGE 42SR250 WIRING DIAGRAM 46

VERSION 5 June 07 PAGE 1

XT250BK.DOC

PHOTO OF MY XT WITH THE SR250 ELECTRIC START ENGINE..


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INTRODUCTION.

I have produced this manual over a few years, as a collection of notes which may be of use to other owners of the XT250. I have had a number of these bikes and have gained considerable knowledge in how to maintain this bike.Should this manual not explain clearly what you are looking for or you require more information please-mail me at ‘[email protected]’ and I will attempt to clarify the description.

DESCRIPTION.

The 1980 to 1983 Yamaha XT250 is a steel framed single cylinder four stroke trial/ road bike with a five speed gearbox and drum brakes, its has 6 volt electric’s and a ‘CDI’ Capacitive Discharge Ignition unit.It has an early monoshock rear suspension design. Previous to this design were twin rear shock absorber designs, these have limited rear suspension travel. The early monoshock rear suspension design has a very long shock inclined at an angle connected to a triangular rear suspension swing arm with no interconnection linkage. This has two advantages, 1) more suspension travel, so the rear wheel can stay in contact with the ground. 2) Less moving parts so less maintenance cost than the later monoshock designs i.e. like the 1985 XT350. The front suspension is conventional twin forks.

The engine is very rugged and gives little trouble if the oil is full and changed regularly. It has a single overhead camshaft than runs in roller bearing and uses rocker arm with tappets. The crankshaft has a geared balance shaft to reduce the vibrations to near zero. It has a 5 speed gearbox and a chain drive to the rear wheel. The rear chain has a tensioner arm and the rear wheel originally a 17 inch alloy wheel is often replaced with an 18 inch wheel for more ground clearance. The drive hub in the rear wheel has rubber shock reducing drive, the rear chain is the 520 size.

The bike is quite light at 113 kg and is quite capable off road as its low weight and powerful 22 BHP high torque engine makes going up hills quite easy. It also sounds like a four stoke and makes a pleasant change from all those 2 stokes out there.

The Bike shares a lot of parts with the SR250, the engine is very similar indeed. If you want to keep your XT running and you come across a SR250 for little money it worth buying it a source of parts and keeping it in your shed until the need arises.The engine has less capacity at 239cc, is reduced in power to 17 BHP, has an electric starter but no kick start and a 12 volt magneto/generator. Oddly though it has larger carb and exhaust header pipe.It is possible to fit this engine into your XT frame. With the use of a hacksaw and a welder.Note; If you lower the front of the SR engine by say 6 to 7mm, the rear is defined by the large swing arm bolt, then you can fit the more reliable SR250 carburettor and the vacuum demand manifold and fuel cock. ...............

During the 1980’s Yamaha also made some 2 stoke trial bikes namely;- the DT125, the DT175 and the DT250. The range also included more 4 strokes;- the XT125, the XT225 ‘Serrow’, the XT350, the XT500, the XT550 and the XT600.


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The XT250 stopped production in 1984 and a later version was produced with a twin cam engine design, basically a baby brother to the XT350.

The current model is a TT250R, which is a more powerful 4 valve engine approx. 37 BHP but produces less bottom end torque. Some models are Electric start only but some have a kick start as well. It has very large diameter front forks and twin piston calliper front brake, so it goes and stops very well.

The XT225 Serrow model is a very popular bike, its based on the XT125 design but bored out to 225 cc, it suits the lighter not so tall rider and is a very popular machine, its lacks the torque engine of the XT250. But it is still a quite capably off roader, it has had a long production run and is a very popular machine.


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YEAR OF MANUFACTURE

I have owned a few of these bikes so we can relate the chassis number to the year of manufacturer. This may be of use if you have a bike which is not registered with the DVLA.

No Plate Frame No. Year of manufacture/ RegistrationKVJ 432Y 3Y3-011558 10/01/1983 Registered in UKTEG 839X 3Y3-011395 02/03/1982 Registered in UKDPX 800W 3Y3-005198 01/03/1981 Registered in UKMKR 977W 3Y3-005087 11/12/1980 Registered in UK

Should you need a letter form the manufacturer to inform the DVLA the year of manufacture this will cost you approx. £25, the address is :- Yamaha Motor (UK) Limited, Sopwith Drive, Brooklands, Weybridge, Surrey, KT13 OUZ. Tel. 01932-358000, Fax. 01932-358030. or www.yamaha.co.uk

DVLA.Should you buy a bike without a current V5, then if you know the registration or the DVLA can find it on their data base, the DVLA will charge you £19 to give you a V5.

However if the bike has not been registered in the UK, then it’s more complex.You need to get a MOT for the bike, then a year of manufacture letter, then a certificate of insurance, then fill in form V55/5 and write of a cheque for £38 for the registration i.e. your V5 and £30 for a years tax.In some cases the DVLA may wish to see your bike, they may charge for this. You can contest this fee as you have info of similar bikes registered in the UK.


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YAMAHA XT 250 G WIRING INFO.

INTRO.The XT 250 wiring diagram is similar to the DT series, in that the battery is not essential to run the engine. The battery powers only the :- Horn, Neutral light, winkers and the Stop and Tail light.

The alternator has three coils, one to give the timing for the ignition, the small coil on the outer side of the stator plate with green and white wires, with a typical resistance of 265 ohms. The second one the left hand side of the stator plate powers the CDI unit with red and brown wires with a typical resistance of 450 ohms, if you remove the Spark plug and kick the engine as fast as you can you should read 24 to 30 volts AC across this coil with no load. The third coil has a tapping part way and has two functions it powers the lights with AC and through a single diode charges the battery. This has a typical resistance of 0.2 to 0.35 ohms.

NOTE: Never store the alternator magnet away from the stator plate, as this allows the magnetic properties to discharge. This is very expensive to correct say £50. If you have to separate them for maintenance then place a large spanner or piece of steel bar across the rotor.The simple test to see if the magnetism is too low, is to place a large spanner across the stator, try to lift up the rotor by only holding the spanner, this is easily possible with a well charged rotor.

The ignition coil has one side earthed and should also have an earth tag from the loom bolted to the frame, ensure this tag is not held of the frame with paint, use a rough sand paper to remove the paint around this bolt hole.

COMMON PROBLEMS.NO SPARK AT THE PLUG.WARNING ensure the plug body is grounded, I use a jumper cable to earth the plug body to the engine.Ensure the coil earth tag is well grounded.Temporarily remove the black and white ‘stop wire’ from the CDI, and check for a spark.WARNING. The coil and CDI system when working correctly can give you a very nasty shock, and once charged the system has to output its last spark. These means if you operate the engine stop switch then kick over the engine one more spark will happen before the system is discharged.

You can check the ignition coil with one piece of wire, remove the orange drive lead which usually joins the CDI output to the coil primary and attached a piece of wire to the coil primary input, hold it on the battery positive terminal for a few second as you remove it from the battery, the spark plug should spark. No spark means either:- a dead coil or plug or plug cap or EHT lead or your battery is flat.

The stator plate coil that powers the CDI is the weak point these are known to fail and are expensive and rare.


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POOR SPARK.The wiring from the stator plate to the CDI is damaged.The wiring from the stator plate wires is not correct to the CDI.The coil is poor.One side the coil is not at chassis i.e. held off with paint.The plug cap needs replacing.The plug needs replacing, set gap to 25 thou or 0.6 mm.The coil on the stator plate does not output enough voltage to fully power the CDI ‘ quite a common problem.’The air gap between the magneto rotor and the timing coil is too small, it must be greater than 32 thou or 0.8 mm.The magnetic charge of the rotor is too low.

THE LIGHTS BLOW.The regulator has failed, these things also fail short circuit which results in no lights working. This item is a zenner diode, its a limiter and should not allow the voltage to increase to such a pint that the lights fail. Should this item fail, un-plug it and drive home with all the lights on and the lowest revs you can manage say less than 2000 rpm. This item sits under the petrol tank and is bolted to the frame.

The lights don’t work and or are dim. You may well have a corroded connection most likely in the handlebar switches, take them apart and clean the contacts with very fine emery cloth. You may have some 12v bulbs fitted, replace them with 6v bulbs. The winkers don’t work well. The cause is too much drop in the loom and not across the bulbs. A common problem with 6 v bikes. Solution add a jump wire from the brown wire ‘ switched power’ to the power side of the winker relay, this involves removing tank and using a soldering iron. This Does work and is great for MOT day, however if the winker switch is poor this can flatten the battery. Another idea is to replace the winker bulbs with LED’s, these would not draw so much current and the special 6v winker relay fitted to this bike should cope with the change in load. I have not tried this idea out yet.

XT WIRING KEY.

Black & White. Engine stop signal, when at ground no spark, when floating sparking.Brown, is switched power i.e. with the ignition switch on +6v is available to power the horn etc.Blue and Blue and red wires, these carry the AC power to the lights. Some confusion here as when in park these lights are powered from the battery.

Light Blue ‘sb; this is the neutral light wiring, take care here all the small lamps in the Speedo are grounded apart from this one which is insulated from ground. Get this wrong and you short out the battery.

Chocolate is the left winkers.Green is the right winkers.Pink is the horn.


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LOOM MODIFICATIONS.

The original loom is not very good, in that instead of running 5 wires for say the ground connection they only run one and bridge it out to 5 wires at each end. The same is true for the switched live wires. This is true for the XT 6 volt loom as well as the SR 12 volt loom.The effect of this is poor winker performance and when the winkers run the tail light pulses.

The cure, for this you need to be able to solder and have some good quality black wire and brown wire, I use ‘19/0.15’ which means 19 strands of 0.15mm per strand, if you can find the PTFE insulation this is better than the PVC type.

Remove the battery.Remove the seat and tank.Remove all of the black tape that is covering the loom over the entire length.Examine the loom for previous damage and poor quality repairs.For example if you find two or three crimp repairs in line connectors make sure they have not cut any of the conductors, if in doubt cut out most of the damage and replace with a fresh piece of wire hopefully in the correct colour. When cutting a wire near a connector leave yourself say 3 inches of wire on the connector to work with and only cut one wire at a time. If you can find heat shrink sleeving use this to cover your solder joint, if not use black insulating tape.

Find the black wires in the main loom, you will find one main wire with say 5 wires joined to both ends. The idea here is to replace this one wire with 5 wires. Note don’t join all 5 wires in one place as this makes for a large bulk of soldering, space them out 1 inch apart along the original thick wire.To be clear here, what I mean is keep the original main wire, cut off the 4 spliced on ends from near the battery, extend all 4 of these wires and one at a time joint them to the main wire 1 inch apart near the battery. At the head lamp end, cut away the 4 spiced on ends leave the main one alone, and attach these 4 ends to you new 4 wires. The result is 5 black wires running the length of the loom.If you stop here this will give you better winker performance and brighter tail light.

You can do similar work with the switched live ‘the brown’ wire.

XT Loom.As the winkers are powered from the 6 volt battery, they don’t work that well. You need to minimise any stray resistance in the loom.

The problem can be in either the power feed of the earth feed. Test.You can test the effect of jumping fresh power to the winkers. Turn on the ignition switch, turn on the winkers and with a piece of wire touch the live side of the winker relay ‘ the brown wire’ with the red lead of the battery. The winkers should respond by speeding up to the normal flash interval. If this shows now improvement, then try jumping a good earth, i.e. with apiece of wire touch the black –ve side of the battery to the case of the winkers. Note you need to use 2 pieces of wire and for this example with the left hand winkers running, jump a new earth to both the left winkers.This test generally show you the improvement you can expect when you have improved the loom. Generally I improve the earth wires and the power wires on these 6v bikes. Only the earth wires on the 12 volt bikes.


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First run an earth lead to the shell of each winkers lamp.Do the black earth wire modification above.

If this is not satisfactory you can do one more thing.The resistance of the ignition switch and 6 ft of wire is not helping the winkers, they only end up with say 5 volts across them.If you are desperate you can jump raw power the ‘red wire’ to the brown connector on the winker relay, first cut off the brown wire. However this leaves power on the relay all the time and can lead to a flat battery. I have done this just to pass the MOT.A more practical approach is to run a new brown wire form the ignition switch straight to the brown pin of the winker relay.


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FIGURE 1. DIRT BIKE WIRING DIAGRAM.


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FIGURE 2. COMPLETE BIKE WIRING DIAGRAM.


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XT250 DIAGNOSTICS.

WHEN THINGS GO WRONG. ENGINE WONT START.

1. Check for fuel in the petrol tank. Find a suitable bowl or jar, pull off the fuel pipe from the tank and check that fuel flows into the Jar. Its well worth fitting an additional fuel filter in line with this pipe, as a further filter should reduce the chance of small particles getting into the carburettor and blocking up the jets.

2. Check for a spark at the plug. Remove the spark plug cap from the plug and remove the plug from the head, use a car jump lead ensure the sparking plug body is grounded to the engine or the frame. Turn the key on and kick over the bike, a large blue spark should result jumping from the plug pin to the outer. On a bright summer day this may be difficult to see. In desperation if you are miles from home and you have a few tools on you, then remove the seat, then the tank, pull out the Black and white wire from the CDI. This removes the emergency stop switch and the ignition key form the circuit. Put the tank and seat back on and try to restart it. Applies to stock XT loom only.

3. If the valve clearances are too tight. Then when the engine warms up the valves don’t shut properly, which results in loss of compression and the engine stops. The inlet valve will run cold but the exhaust runs very hot and is prone to expansion. If you have some wear in the rocker shafts then don’t set the Exhaust valve up for the exact 6 thou, add a few thou for good measure say 8 or 10 thou. This will then allow the engine to run.

OBSERVATION.The most common fault is dirt in the fuel blocking up jets in the carburettor.The second is a sticky float, which either sticks closed so no fuel so engine wont start or stick open and fuel flows down the road. Use a screwdriver and tap the side of the carb this should loosen the float and make it work.The third is no or low fuel flow through the fuel tap, pull off the pipe and see if fuel flows freely into a jar. The filter built into the fuel tap can clog up with rust and paint chips. If you’re at home drain the tank remove the tap and clean the tank with lost of water.If your on the road, find a foot pump and blow air back into the fuel tank, this will blow the debris free of the filter and should get you home.

If you are parking the bike for a few weeks without use, then a few 100 yards from home turn off the fuel tap and run the engine until it stops. This ensures the float chamber is empty, which means the last fuel does not gradually evaporate in the carb and leave a sticky residue behind waiting for you to start the engine and suck through the jets blocking them.

If you think your electric’s are giving you trouble, here are a few things for you to try.

1. It is possible to miss-connect the 3 coils on the stator plate to the CDI I have done this, this results in the same problem the engine wont rev up, check the colour of the wires form all three coils, see the diagrams on page 7.


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2. If you have a strobe light, ' Halford’s sell these' you need to do this test in the near dark, plug this strobe light in series with the sparking plug. Remove the plastic cover from the alternator, paint some red paint on the flywheel marks to make them stand out. Start up the bike and look at the flashing light it must always illuminate the red marks, if the timing is out it will move about the flywheel. If this is true then the small external coil needs to be checked or replaced as this supplies the timing info to the CDI.Also all engines have what is called an advance and retard curve, this means some movement of the timing is required at low engine revs, so this will be displayed in the strobe test, as long as the movement is consistent with low RPM then its OK. This is difficult to explain, if you have a bike or car that woks then you can look at a working example first.

3. The coil may be poor, it should produce a good spark up to 3 mm. some coils have the wrong resistance for the CDI to power, try another coil.

For the engine to over heat indicates one of the following problems. 1). the timing is wrong. The rotor is key onto the crankshaft with a woodruff key, this ensures the correct magnetic pulse position relative to the piston position. These woodruff keys can fail so the rotor can be misplaced.If this key is good then it’s more likely an electrical problem. Replace to stator plate or the CDI.

2). The carb is running far too lean, check for blocked jets or previous owner changing the jet sizes.

3). The tappets are set to tight. This can burn the exhaust valve. Position the engine at Top dead centre and adjust the tappets for the required few thou of slack. See table in the last chapter.

4) Check the height of the fuel in the float chamber. Assuming the carb drain screw works, then find a piece of transparent plastic tube and plug it on to the overflow port, undo the drain plug and fuel will flow into this tube. Hold the tube upwards and within say 20 seconds the fuel level within the carb will be the same as the level in your pipe. It must be say 1mm below the float chamber gasket position.

4b) Check the height of the fuel in the float chamber. Assuming the carb drain screw does not move. Remove the seat and lessen off the bolts that hold the air box, remove the carb from the inlet rubber. Loosen the clip on the engine carb input port and remove the carb, slacken off the 2 throttle cables and remove the carb from the bike.Using a small plastic tube and funnel and water, connect he tube up as the petrol tank and fill the funnel with water, until the carb stops consuming water, then remove the float bowl without disturbing the position of the carb and look a the water level. As the float is no longer in the float chamber you have to allow for it displacement, so the water level should be within 4mm of the flat bowl gasket.

To adjust the fuel height you have to bend the tab on the arm of the float that operates the fuel valve. Be careful a very small bend say 0.25mm has a large effect on the fuel level say 4 mm. bend the tab in very small increments and recheck the fuel height.

When you are satisfied with the fuel level, remove all the water, reassemble the carb and refit it to the bike.


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FIGURE 3. THE STATOR PLATE AND CDI.


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CDI MAGNETO PARTS LIST.

Ref Part No. Description Quan1 (3Y1-85500-20-00) CDI MAGNETO ASSEMBLY 12 (3Y1-85550-20-00) ROTOR ASSEMBLY 13 3Y1-85509-20-00 BASE, MAGNETO 14 31G-85512-20-00 COIL SOURCE 2 15 3Y1-85519-20-00 SPACER 16 3Y1-81343-20-00 COLLAR, COIL FTNG 27 3Y1-85513-20-00 COIL, LIGHTING 1 18 3Y1-85580-20-00 COIL, PULSER 19 3Y1-85515-20-00 LEAD WIRE ASSEMBLY 110 445-81328-20-00 CLAMP 111 ¢3Y-18552-82-00 CLIP 112 98501-05030-00 SCREW, PAN HEAD 213 98501-05035-00 SCREW, PAN HEAD 214 98580-05012-00 SCREW, PAN HEAD 215 97601-04106-00 SCREW, PN/HD.W/WSHR 216 98580-06020-00 SCREW 217 92990-06200-00 WASHER 218 93102-25226-00 OIL SEAL 119 93211-19413-00 O-RING 120 3Y1-85540-20-00 CDI UNIT ASSEMBLY 121 97313-06016-00 BOLT, HEXAGON 222 92995-06100-00 WASHER, SPRING 223 ¢90-46208-06-30 CLIP 1


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FINDING THAT SPARE PART.

My local Yamaha dealer has not failed me yet, every part I ask for he can find the part number and place it on order, it always turns up within 5 to 10 days, not bad for a bike that went out of production 22 years ago.This is partly due to the fact that the SR250 which shares a lot of common parts with the XT250 has had a very long production run, from 1980 until 2004.

If you cant find that part or the new price is just too high then go visit ‘ebay.co.uk’, I have found many parts on this site at reasonable prices.

Other similar bikes that can supply parts that may fit or can be made to fit with a little work.

Part Will Fit straight in Will require work to fit Worth ConsideringSpeedo and tacho XT125 DT125/175/250 XT350, XT600Head lamp DT125/175Head lamp Brackets

None DT125R DT250MX

Loom None DT125LC not R SR250Switches DT125/175 & DT125RRear Wheel SR250 ‘but 16

inches’XT350 but change the sprocket

DT125/175KX125/175 Kawasaki

Kawasaki KLR250

Front wheel DT125/175/250Exhaust Header Micron. CRD, BSM,

PredatorKLR250, with some welding

Kawasaki KLR600 with a SR250 front piece welded in.

Exhaust silencer Micron. CRD, BSM, Predator

Rear Axle SR250??Brake shoes SR250??Seat NonePetrol Tank NoneFront Forks None DT125LC, or DT250

drum brake version, will need yokes

Rear Shock None


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CONVERTING TO A 12 VOLT SYSTEM.

The original XT circuit diagram is very similar to the early DT125, i.e. magneto powered CDI and 6 volt ac lights, with 6v dc powered horn, winkers and stop lamp. This is OK but has disadvantages; The winkers don’t work that well, due to excessive volt drop in the wires and

connectors. If the engine stops the lights go out. You have to kick the engine over quite hard to produce a spark

If you can find a donor SR250 its worth buying as a source of spare parts. It has a full 12 v dc system with battery powered lights and the CDI. Its only disadvantage is that if the battery is flat it wont start, you would have to charge up the battery first.The advantages are: powerful headlight, lights work when the engine stops. The winkers work, and in the winter you can fit electrically heated gloves. But best of all it starts a lot easier as the voltage applied to the spark plug does not depend on how hard you kick the engine over.

XT250G 12 Volt Conversion.

If your ignition side is all working.Then you would only need to replace one coil on the stator plate, the rectifier and all the bulbs and the battery to give you 12 V, remove the over voltage protector. You would need to move one wire to change the headlamp from ac power to switched dc power. This would cost you less in terms of parts, assuming you dont have a donor SR250 in your shed.I have not done this half conversion. you would need to confirm the 12 volt coil will physically fit the stator plate. This has the advantage of magneto powered ignition, i.e. you can drive home with a flat battery.

If your ignition side is Not working.You will need a donor bike the SR250 is favourite.

Remove from your bike:- Battery, Loom, Ignition Coil, CDI, Rectifier, Over Voltage Limiter, all Bulbs, Rotor and Stator plate from engine ‘ Note you will lose oil use a drip tray.’ a Rotor removal tool helps its the same part number as a DT125.

Strip all these parts from your SR250 after confirming they all work.

Then you would need to replace the stator plate and the rotor, the rectifier the CDI and the coil, both handlebar switches, all the bulbs and the battery to give you 12 V.You will have to make up plates to hold the CDI, the Coil and the rectifier.Note: on the SR the 12 volt power is switched to the CDI via the right hand switch via the red and white wire, this is why you need to change the switch over. You can still use your original coil if you wish, but you would need to mount it on an insulating glass fibre plate.

Kick over the bike and you should get a really healthy spark, start the bike up and confirm the 12v battery has 12.8 v to 13.2 volts with the engine revving.I have now done this conversion to 2 bikes with complete success.


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MIKUNI CARBURETTOR.

This item gives more trouble than any other part on this bike.

Common faults:Petrol floods out of the Carb. Turn off the fuel and wash excess of the engine and floor with water.Use a screw driver and tap the carb body, this should loosen the sticky valve and stop the fuel flooding out. If not remove carb and strip down as per description above??.

Engine wont start. Suspect no fuel in float chamber. If you are in luck you can undo the small screw in the base of the float chamber this should allow the fuel in the float chamber to leak away, if none comes out then the float chamber is dry. This can be caused by, 1) no fuel in tank, 2) fuel tap broken or blocked, 3) fuel level valve in carb has stuck closed.Assuming its 3, then Use a screw driver and tap the carb body, this should loosen the sticky valve and allow the fuel flooding out. if not remove carb and strip down as per description above??.

If you have no air box, then release the input clamp on the rubber engine input port and remove the carb, loosen off the two throttle cables and remove the carb to the bench for work.If you still have the air box fitted then you have more work to do. Remove the Seat. Remove the battery. Remove the 3 bolts that hold the air box in position, undo the clamp on the rubber that connects to the air filter, push the air box away to the rear of the bike, then continue to remove the carb as detailed above.

The Mikuni carb is conventional in operation. However due to the large inclined rear shock absorber the carb does not have the control cable going into the top, but on the side, it has 2 cables one to open the throttle and one to close it. It also has an external throttle pump.

The four small screws that hold on the float chamber are best replaced with Allen head screws, this allows you to remove the float chamber with the carb still on the bike.Useful things you will need are: Find a container to put all the parts in. A short length of hose with a small funnel fitted. A bottle of water.

Undo the thread linkage on the throttle pump. Remove the float chamber.Clean up inside. Take care not to lose the plastic piece that sits right in the bottom of the chamber.Hold the float chamber in a vice, wrapped in a rag to avoid damage and try to remove the drain screw, this is usually very difficult. If you can move it fit a new one with a small drop of grease on the thread.Fill the chamber with water, operate the throttle pump, some water should bouble out of the output port. ?? add notes how to correct this.

Remove the pilot jet and blow air through it.Remove the main jet and the tube above it, this had 2 sets of 4 holes in it, usually these get blocked, blow air through these 8 holes, hold them up to the light to see that they are clear.

Support the carb at 90 degrees to the bench with a small socket, and with a small hammer and centre punch lightly tap out the shaft that hold the float in place. The float should be


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dry and float when placed in a bowl of water. Note the very small clip that attaches the float movement tap to the input fuel valve.Use a cross head screw driver and remove the small plate that holds the input fuel valve in place. Try and remove this valve, these dont always come out?? the black rubbery surface may have some contamination on it, clean it off with a rag. If this surface is marked, then replace this valve as this will cause flooding and petrol loss.

The carb body has a few small diameter drillings that can get blocked. Its best to blow out dirt with a foot pump, if this fails then find a piece of thin wire and try and poke out the dirt.

TIP. If you have a dirty carb or and engine that just wont start. Buy some ordinary vinegar and soak the carb parts for 48 hours. It’s best to remove the float bowl and jets and remove the float and valve that’s lets the fuel in. Don’t soak the rubber parts i.e. the float and the fuel valve. Than put all parts in soak. This will soften up most of the dirt and the yellow residue that goes hard and blocks up jets and passageways. Now soak the parts in water for ten minutes. Using either a foot pump or the LIDL £5 pump, pump out all the passageways. Reassemble the carb.Now with a bit of luck the engine will start.


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HOW TO FIX YOUR CARB

Although you can buy individual parts for this Carb from your local Yamaha dealer. It is also possible to buy a complete kit of parts from a firm called Keyster.

I bought mine on eBay from Germany, from a motor bike shop called ‘Motorradbay’ for 25 Euros plus post & packing came to 34 Euros which is approx £23.

The KEYSTER kit of parts for the XT250 is part No. KY-0218 for the Mikuni carb with Yamaha part No. 3Y3-14101-00. This kit is very good it has all the gaskets and jets and the fuel valve, some 19 parts in all.

The KEYSTER kit of parts for the XT250Ref Part No. Description Quan11 3Y1-14184-00-00 GASKET, FLOAT CHAMBER 126 2H0-14190-20-00 NEEDLE VALVE ASSEMBLY 110 ¢16-81411-66-50 NEEDLE 17 164-14137-00-00 CLIP 1XX XX AIR SCREW ‘ NOT SHOWN IN SKETCH’ 15 3H1-14589-00-00 SPRING AIR ?? 166 3Y1-14940-00-00 DIAPHRAGM ASSEMBLY ‘ PLUNGER’ 167 3Y1-14589-00-00 SPRING 133 137-14143-33-00 JET, MAIN #165 (#165) 19 3Y1-14142-17-00 JET, PILOT #17.5 (3Y1-14142-17-A0) 134 583-14561-00-00 O-RING 2 ??36 2N6-14227-01-00 WASHER 115 3Y1-14536-00-00 GASKET 1

56 2H0-14272-00-00 VALVE, CHECK SEAT 162 91490-12012-00 PIN, COTTER 114 ¢3Y-11415-30-00 WASHER MAIN JET 157 2H0-14195-00-00 WASHER, NEEDLE VALVE 1

??? MUST CHECK THIS

The real problem is lack of any detailed information on how to repair your 30mm Mikuni.the blocked holes are not just the jets but drillings in the casting.Plus how do you fix a bolt that wont budge, or a fuel valve you cant remove.


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PHOTO 1. KEYSTER CARB KIT.


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FIGURE 4. MIKUNI CARB EXPLODED VIEW.


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PARTS LIST FOR MIKUNI CARBURETTOR

Ref Part No. Description Quan1 3Y1-14101-00-00 CARBURETTOR ASSEMBLY 1 12 ¢3Y-11411-22-50 THROTTLE SLIDE, VALVE THROTTLE 13 (3Y1-14174-00-00) CAP, PLUNGER 14 3Y1-14171-00-00 PLUNGER, STARTER 15 3H1-14589-00-00 SPRING 16 2N6-14227-01-00 WASHER 17 164-14137-00-00 CLIP 18 2N6-14918-01-00 RING 19 3Y1-14142-17-00 JET, PILOT #17.5 (3Y1-14142-17-A0) 110 ¢16-81411-66-50 NEEDLE 111 3Y1-14184-00-00 GASKET, FLOAT CHAMBER 112 3Y1-14981-10-00 BODY, FLOAT CHAMBER 113 3F9-14118-00-00 CAP 114 ¢3Y-11415-30-00 WASHER MAIN JET 115 3Y1-14536-00-00 GASKET 116 ¢3Y-11459-20-00 SCREW 117 92901-04100-00 WASHER SPRING 118 ¢3Y-11427-60-00 LEVER 119 ¢3Y-11427-50-00 SPRING 120 ¢3Y-12445-30-00 SCREW 221 ¢3Y-11429-10-00 BRACKET 1 122 3A3-14173-00-00 COVER, PLUNGER CAP 123 98580-06012-00 SCREW, PAN HEAD 124 92995-06100-00 WASHER, SPRING 125 156-14135-00-00 SPRING, PLUNGER 126 2H0-14190-20-00 NEEDLE VALVE ASSEMBLY 127 537-14186-00-00 PIN, FLOAT 128 2H0-14146-00-00 PLATE 129 98511-04006-00 SCREW, PAN HEAD (98501-04005) 130 583-14589-00-00 SPRING 131 93501-08001-00 BALL 132 3H1-14185-00-00 FLOAT 133 137-14143-33-00 JET, MAIN #165 (#165) 134 583-14561-00-00 O-RING 235 3H1-14148-00-00 PIPE 136 ¢3Y-11414-13-80 NOZZLE MAIN 137 583-14594-00-00 NUT 138 3Y1-14175-00-00 LEVER, STARTER 1 139 24U-14103-00-00 THROTTLE SCREW SET 140 3F7-14934-00-00 SPRING, THRTL STOP 141 3Y1-14215-00-00 SHAFT, THRTL LEVER 142 ¢3Y-11429-20-00 BRACKET 2 143 (3F7-14265-00-00) COLLAR 144 2A2-14997-00-00 SEAL 145 3Y1-14131-00-00 SPRING, THRTL VALVE 146 1A8-14953-00-00 WASHER 147 98580-05010-00 SCREW, PAN HEAD 2


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48 3Y1-14571-00-00 BRACKET, THROTTLE 149 98503-04014-00 SCREW, PAN HEAD 1050 92901-04100-00 WASHER, SPRING 1051 584-14956-00-00 WASHER 152 2F5-14115-00-00 PLUG, SCREW 153 ¢3Y-11415-80-00 TOP MIXING CHAMBER 154 3Y1-14197-00-00 PIPE 155 3Y3-14196-00-00 PIPE, OVERFLOW 156 2H0-14272-00-00 VALVE, CHECK SEAT 157 2H0-14195-00-00 WASHER, NEEDLE VALVE 158 3Y1-14992-00-00 ROD 159 2H0-14992-00-00 ROD 160 3Y1-14933-00-00 SPRING, DIAPHRAGM 161 2H0-14534-00-00 COLLAR 162 91490-12012-00 PIN, COTTER 163 2H0-14227-00-00 WASHER 264 (3Y1-14905-00-00) LEVER, STARTER 165 3Y0-14918-00-00 RING 166 3Y1-14940-00-00 DIAPHRAGM ASSEMBLY 167 3Y1-14589-00-00 SPRING 168 3Y1-14936-00-00 SEAT, SPRING 169 12R-14191-00-00 PLUG, DRAIN 170 3Y1-14561-00-00 O-RING 1XX XX AIR SCREW ‘ NOT SHOWN IN SKETCH’ 1


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YEARLY MAINTENANCE.

LUBRICATE THE SWING ARM BEARINGS.

If you have done this last year then it will only take you one hour.

If this has not been done for a few years it may take 2 to 3 hours.

If the swing arm bearings need to be replaced this can take 6 to 8 hours....

Drain and refill the engine oil, with new filter.

Oil the air filter element

Check the battery for the correct water level, Charge it up, Dont store the battery flat as this does damage. Remove from bike, keep it indoors and trickle charge it with a 40mA.

Check the slack in the rear chain and lubricate. Note if you can pull one link off the middle of the rear sprocket more than the height of the sprocket teeth then the rear chain and possibly the sprockets need to be replaced.

Check all light bulbs work.

Check the tyres are inflated, and centrally located on the rims and have at least 1.2 mm of tread all over the tyre. Check the side walls have no splits in.

Remove each wheel in turn and examine the brake linings for wear, and adjust the cam angle if required. With the brakes full on, the operating lever must be at 90 degrees to the operating cable for maximum efficiency.

Check the wheel bearings for slack.


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YEARLY SWINGARM LUBRICATION WITHOUT REPLACING ANY PARTS.

Remove the seat, fuel tank and battery.With the bike still on the ground, loosen off these bolts.Rear wheel spindle.Both bolts at either end of the rear shock absorberThe major bolt that goes through the rear of the engine and the swing arm bushes.All of the engine bolts, 4 on the front bracket, 3 on the head bracket and 2 at the rear of the gearbox.

Place the bike on a stand which allows the rear wheel to just be off the ground.

Remove the chain, release the rear brake linkage and remove the rear wheel.Remove the major bolt that goes through the rear of the engine and the swing arm bushes, the 2 small M6 screws that hold on a small plate near the main bolt. If this is difficult then slacken off all of the engine bolts especially the 2 at the rear of the gearbox.Remove Both bolts at either end of the rear shock absorber. The one that links with the top of the swingarm triangle can be very difficult to remove. Its usually a Roll pin with a split link and not a bolt, these are stronger than bolts.Remove the swing arm from the bike.

The swing arm bearings are made of a fibrous material, inside of these 3 bushes are 2 steel tubes, these are chrome plated when new. Inside of these two tubes sits the main bolt. 4 end plates one with shims make up the correct width. Also on the swing arm is a nylon piece that protects the arm from loose chain damage.The two tubes should rotate within the bushes and slide out with only finger pressure.

If you re lucky the two tubes have pushed out easily, examine the bushes and the steel bolt for wear, if none is evident, apply lots of Castrol LM grease and reassemble. This is not easy and you run out of hands. Put on the nylon piece the 4 off spacers and the fish plate ‘ an oval shaped plate with 2 off m6 holes in and a large hole for the main bolt. Offer the whole lot up to the bike and with a well greased main bolt push it into position. a light hammer may well be required. Ensure the bolt head is on the left hand side of the bike, i.e. the nut goes on near the rear brake switch.Rotate the fish plate and fit both the 6 mm screws.Now fit the rear shock with grease on both bolts, fir the swing arm bolt first.This task is a lot easier with 2 people.Do up all of the bolts not forgetting the engine bolts and the 2 at the rear of the gearbox.Now fit the rear wheel.The side to side slack at the rear wheel should not be noticeable i.e. less than 1 mm. greater than this will fail the MOT.If all is good then refit the chain and the rear brake lever.................................


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If some slack is evident, check to see if its end float or bearing slack. End float is corrected by adding a shim to one of the bearing end caps, you can buy these from Yamaha they are I effect a very thin washer say 20 thou thick. Remove the swing arm, remove one end cap add one shim and refit and check for slack.If you dont fit the rear shock this makes it easier to check for slack. Also if too much shim is fitted then resistance is felt when trying to move the swing up an down.

If the bearing or the bolt are worn then new parts are required.

To change the 3 bushes is a 6 to 8 hour task.Buy a set of bushes and a large bolt and washers plus an abra file.An Abra file is a clever gadget, it fits in a conventional hack saw frame but its a thin say 1/8 inch round file.

Remove the swing arm from the bike.Remove the two steel tubes. If you cant drift them out then you have to pull them out with the long bolt and washers and a few large sockets used as spacers. NOTE: If these are seized in position this may take 1 hour each.

Now using the abra file slide the file through the bush, attach to the hack saw frame and saw or file you way through the bushes. this only take 10 minutes.

Clean up the steel frame and fit the bushes. This is also done with the large bolt and washers, it is not possible to hammer the bushes into position as they will distort and break up.Using the bolt and washers and a few large sockets by tightening the bolt you can gradually draw the bush into the tube in the frame. This takes some time as the bolt runs out of thread and washers or sockets have to be removed to use the bolt in its threaded portion. This will take you 1 hour or 2.Once all 3 bushes are in place you can reassemble the swing use plenty of grease.

NOTE: the Yamaha diagrams show 3 bushes fitted, however it is possible to fit 4, to give extra support in the chain area.


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FIGURE 5 SWING ARM EXPLODED VIEW.


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PARTS LIST FOR SWING ARM ASSEMBLY

Ref Part No. Description Quan1 3Y1-22110-00-33 REAR ARM 12 3Y1-22184-01-00 BUSH ‘FIBRE’ 13 3Y1-22123-01-00 BUSH 1 ‘FIBRE’ 24 3Y1-22124-01-00 BUSH 2 ‘STEEL TUBE’ 25 240-22127-00-00 SHIM 16 322-22128-01-00 COVER, THRUST 1 37 93109-22019-00 OIL SEAL, SDO-TYPE 18 3Y1-22151-00-00 SEAL, GUARD 19 3Y1-22318-00-00 GUARD, CHAIN 110 97313-06016-00 BOLT, HEXAGON 311 92995-06100-00 WASHER, SPRING 312 92901-06600-00 WASHER 313 2N6-22141-00-00 SHAFT, PIVOT 114 90201-14218-00 WASHER, PLATE 115 90185-14070-00 NUT, SELF-LOCKING 116 3Y1-22311-00-00 CASE CHAIN 117 98503-06014-00 SCREW, PAN HEAD(92502-06016) 218 92995-06100-00 WASHER, SPRING 219 90201-062A8-00 WASHER, PLATE 220 3Y1-21329-00-00 PLATE 121 98580-06012-00 SCREW, PAN HEAD 222 92995-06100-00 WASHER, SPRING 223 92901-06600-00 WASHER 224 3Y1-22179-00-00 ARM, TENSIONER 125 93104-14044-00 OIL SEAL 226 ACC-11130-00-25 TENSIONER (2N0-22178-00-00) 127 1W1-22187-00-00 GUIDE, CHAIN 128 98501-05040-00 SCREW, PAN HEAD (98502-05040) 229 92990-05100-00 WASHER, SPRING 230 95380-05600-00 NUT 231 90109-10483-00 BOLT (90109-10533-00) 132 90508-35350-00 SPRING, TORSION 133 120-27430-02-00 RR FOOTREST ASSEMBLY 1 234 120-27432-02-00 BRACKET 1 135 120-27433-00-00 COVER, REAR FOOTREST 136 90201-20279-00 WASHER, PLATE 137 120-27431-00-00 FOOTREST, REAR 1 138 90240-06009-00 PIN, CLEVIS 139 95301-12700-00 NUT (95302-12700) 140 91490-16020-00 PIN, COTTER 1


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Space for photo of rear shock.


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PARTS LIST FOR REAR SHOCK ASSEMBLY

Ref Part No. Description Quan1 3Y1-22210-01-00 SHK/ABS ASSEMBLY, REAR (3Y1-

22210-00)1

2 (3Y1-22401-00-00) DAMPER SUB-ASSEMBLY 13 3R4-22226-00-00 BUSH, SHOCK ABS LWR 14 90380-12051-00 BUSH, SOLID 25 (1W1-22493-00-00) BUMP, STOP 16 3R4-22228-00-00 SUPPORT, BUMP STOP 17 90206-14067-00 WASHER, WAVE 18 (3Y1-22409-00-00) UPPER BRKT SUB ASSEMBLY 19 1YW-22216-00-00 BUSH, RR SHOCK ABS 110 90170-20211-00 NUT 111 3R4-22213-00-00 SEAT, SPRING UPPER 112 3Y1-22212-00-00 SPRING 113 3R4-22214-01-00 GUIDE, SPRING 1 (3R4-22214-00) 214 ¢3Y-12222-40-00 115 ¢3Y-12222-30-00 116 93440-48079-00 CIRCLIP, OUTER 117 90109-10554-00 BOLT 118 90201-10126-00 WASHER, PLATE 119 95601-10100-00 NUT, U (95602-10100-00) 120 1W1-22128-00-00 COVER, THRUST 1 221 90240-12075-00 PIN, CLEVIS 122 92990-12600-00 WASHER, PLATE 123 91401-30030-00 PIN, COTTER 124 3Y1-22179-00-00 ARM, TENSIONER 125 93104-14044-00 OIL SEAL 226 ACC-11130-00-25 TENSIONER (2N0-22178-00-00) 127 1W1-22187-00-00 GUIDE, CHAIN 128 98501-05040-00 SCREW, PAN HEAD (98502-05040) 229 92990-05100-00 WASHER, SPRING 230 95380-05600-00 NUT 231 90109-10483-00 BOLT (90109-10533-00) 132 90508-35350-00 SPRING, TORSION 133 120-27430-02-00 RR FOOTREST ASSEMBLY 1 234 120-27432-02-00 BRACKET 1 135 120-27433-00-00 COVER, REAR FOOTREST 136 90201-20279-00 WASHER, PLATE 137 120-27431-00-00 FOOTREST, REAR 1 138 90240-06009-00 PIN, CLEVIS 139 95301-12700-00 NUT (95302-12700) 140 91490-16020-00 PIN, COTTER 1


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CYLINDER HEAD

The cylinder head contains two valves with two rockers, on each rocker is a small screw called a ‘tappet’, which needs to be adjusted for the correct gap.If the engine is low on oil or the oil pump is worn, the most likely area for wear is the rockers in the cylinder head.The good news is that this area can be overhauled without taking the engine out of the frame.

If you have just bought a bike that has not run for some time, then remove the tappet covers and the large plate of the timing sprocket and apply lots of oil to all moving parts including the head bearings. As on start up the head is the last item to get any oil.

Assuming the rockers or tappets are making a lot of noise and replacing the tappets has not solved the problem. then further work is required.

Remove the Seat, battery and tank.It is easier to do this work with the bike supported on a stand for this task.

Remove the engine side cover and the round cam shaft side cover. remove the spark plug, remove both tappet covers.Using the kick starter or a 17 mm spanner on the flywheel nut, rotate the engine forwards until top dead centre is reached. This can be confirmed by many methods.1) The piston is at the top of the stroke and both tappets have slack.2) Or the marks on the flywheel line up with the dink in the casting. 3) Or the mark on the large camshaft gear is at 12 o’clock.

Using two sets of spanners, hold the flywheel nut still using a 17 mm spanner, and using a spanner xxMM undo the cam shaft nut. Should the engine move slightly reposition by rotating the flywheel.Remove the cam chain tensioner from the engine.Slip a piece of wire or sting through one link of the cam chain and tie it to some part of the frame.Remove the large cam shaft bolt and the large cog.Using a light hammer and a drift or a 1/4 inch socket extension, tap the bent tabs flat on the two positions, remove the 3 off 6 mm bolts.Remove both tappets and the lock nuts.By inserting an 8 mm bolt into each rocker they can be removed.By inserting an 10 mm bolt into the cam shaft it can be removed.All these removed parts need to be placed in a tray and in the correct position, so as to avoid confusion during re-assembly.

Examine the lobes on the camshaft, if wear lines are present in the cam shaft then it needs to be replaced.Examine the foot of each rocker if this is worn they need to be replaced.Examine the wear of the rocker spindle and the rocker, if significant they need to be replaced.

Yamaha noticed some significant wear occurring on the early design of rocker foot and the design changed to a wider foot, this reduced wear on both the rocker foot and the camshaft.


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These parts would be very expensive if bought new at your Yamaha dealer. say approx. £100.However the SR250 head is the same so you can either replace the entire head or just replace the damaged parts as you see fit.If you cant find a new or replacement cam shaft, then rub off the sharp edges with a stone and fit the newer design of rockers with the larger foot, this should keep the engine going for say a year or 2000 miles before its next overhaul.

It is just possible to remove the head with the engine still in the frame, but it tough, as the 4 head bolts are very long and hit the frame and the coil. you will need to remove one head bolt o remove the exhaust rocker shaft. On no account just remove one head bolt as this could distort the head. Undo all 4 of them plus the 2 Allen screws, but leave them in place.That said having gone to all this trouble you might as well remove the head and decoke the valves. Its up to you.

Reassemble is the reverse procedure. The rockers are handed so you cant put the wrong one in the wrong end.Remember to knock over the tab washers.Refit the large cog and put in the bolt finger tight. Fit the tappets finger tight. Double check the mark on the large cog is at 12 o’clock and the engine is still at top dead centre and you have some slack in the tappets. refit the cam chain tensioner.Triple check the position of the cam shaft and the engine are correct. one tooth out will look like an error of 5 mm on the cam shaft cog, you should see no error at all.If OK then do up all the bolts. On the cam chain tensioner, the idea is to tighten it up until the moving plunger ‘the 2 mm stainless steel shaft’ is flush with the outer large nut.Now you can carefully rotate the engine and listen for nasty noises. Rotate it a few cycles and once again check the crankshaft position relative to the cam shaft position.


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FIGURE 6. THE CYLINDER HEAD.


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CYLINDER HEAD PARTS LIST

Ref Part No. Description Quan1 3Y1-11110-00-00 CYLINDER HEAD ASSEMBLY 12 93440-12052-00 CIRCLIP 23 90153-06045-00 SCREW, HEXAGON 14 90430-06014-00 GASKET 15 3Y1-11133-10-00 GUIDE, INTAKE VALVE 26 583-11127-00-00 ABSORBER 3 37 583-11127-00-00 ABSORBER 3 18 3Y1-11181-09-00 GASKET, CYLINDER HEAD 19 99530-14016-00 PIN, DOWEL 210 90430-14131-00 GASKET 111 90105-10140-00 BOLT, WASHER BASED 212 90105-10139-00 BOLT, WASHER BASED 213 90201-10128-00 WASHER, PLATE 314 91316-08050-00 BOLT 215 3Y1-11185-00-00 CYLINDER HEAD SIDE 116 93211-06635-00 O-RING 117 98506-06025-00 SCREW, PAN HEAD 218 3Y1-11186-00-00 COVER, CYLINDER HEAD INLET 119 3Y1-11187-00-00 COVER, CYLINDER.HEAD EXHAUST 120 93210-57634-00 O-RING 221 91316-06020-00 BOLT, SOCKET HEAD 422 90109-06556-00 BOLT 123 3Y1-1111F-00-00 PLATE 124 97013-06012-00 BOLT 225 90215-06162-00 WASHER, LOCK 126 NGK-BP7ES-00-00 SPARK PLUG, SPARK (NGK BP-7ES) 1


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EXHAUST.

The mild steel stock Exhaust is prone to rust and it quite a heavy and restrictive unit, it is however nice and quite so is most suitable for greenlane use.

A few after market exhaust are available but these are very pricey at £250.

Micron make a stainless system, which is light and should last well, its rather loud though.CRD and Predator make a similar system.

If money is tight then when your stock exhaust rots away you have real problems. You can weld it up for a while but at some point you are looking for a cheap alternative exhausts.

You can make up a cheap header pipe from the first 3 inches of an SR250 exhaust and Kawasaki KLR600 header pipe. Both of these are available from breakers and ‘eBay’, these parts should only cost you £10.The Kawasaki header has an odd oval input port which you can saw off, only lose approx. 1 inch of the pipe and discard the flange.With the SR header pipe you only want the first 3 inches and the flange.Now trim to fit the engine for position and weld the two pieces together. As the SR pipe fits inside the Kawasaki pipe with a 2 to 3 inch portion of both tubes overlapping the chance of leaks quite low.

If you can find a Kawasaki KLR250 header pipe. This can be modified to fit, assuming you can weld. What you need to do is to cut of the almost straight part and weld it back on the other way around, i.e. the part that was near the head bend piece is now at the back near the silencer. This works very well.

So now you are looking for a silencer. I have tried out a few 2 stroke cans and although you can make them fit they are far too loud. My best success was with an early 1980 SR250 can which fitted straight on and was nice and quite. I have also fitted one can of a Yamaha TDM850, which is OK a little loud.


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FRONT FORKS.

This is one part I have not ever taken apart. Yet. One good trick however should you have leaking seals is not to follow the manual and just replace the seal without diss-assembly of the fork leg.

Place the bike on a stand, remove the front wheel, remove the offending fork leg. Remove the gaiter if it has one. Clean the area around the seal. Very carefully using a small screwdriver or pair of pliers remove the retaining clip, ‘ take great care not to scratch the Chrome finish’ then remove the top dirt guard. Now you are looking at the top face of the oil seal.

With a second person to assist and a piece of wood say 18 inches by 6 inches by 1 inch. with your assistant holding the fork leg vertical, you place the piece of wood over the top of the fork leg and put all of your weight on it, i.e. try to lift your feet of the ground. This sudden application of force will compress the fork leg and the oil has no wear to go so it takes the only route out by lifting the seal up the fork leg. Once the seal is out of the holding bucket you can remove by hand. If this not work, add some oil into the fork leg, yours could be dry.Clean off the fork leg, and fit the new seal, then the dust guard and finally the spring clip.Then fit the fork and wheel into the bike.This whole task should take 1 hour.

The forks are basically two major parts which are held together with a bolt form underneath. If you can remove the ‘alley key bolt’ then you can slide the chrome stanchion out of the cast aluminium leg. You have to use a slide hammer action to split apart these two major pieces.However this still leaves you the chrome tube with the internal spring. If you wish to disassemble this further then you need to remove the circlip that retains the spring. Best do this first, however you can put the chrome stanchion backing the bike and using a home made steel bracket bolted to the top fork pinch bolt with a third hole in the middle of the fork leg, fit a bolt and nut through the bracket which should touch the middle of the fork tube, use a 6mm steel bolt. Force the bolt down with two spanners, this will push the spring and the cap downwards say 1mm, then the circlip is not under pressure, with a bit of luck and a small screw driver you can get the circlip out, don’t lose it. Now the stanchion can be taken apart. The rebuild the reverse of the same process.

.....................I have met two people now who have replaced the front forks with different Yamaha one’s, so that they can have a disk front brake. Both chaps have fitted the XT350 set of forks. Some work is required to the XT350 yoke set in order to obtain the correct amount of steering i.e. the bikes turning circle and to limit the steering lock so that the petrol tank is not dented.

I have seen XT500 with a similar conversion they use either DT125R forks or XT600E forks, ‘the post 1992 model has a twin pot front calliper’.

I have not tried this modification out yet but it on my list of thing to do. I am not sure of the effect of having longer fork legs, these may need to be machined down to the original length for the ‘XT250’ so as not to affect the bikes handling.


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If you wish to keep the gold look alloy wheels and still want a disk brake, then look at a Kawaski KX125/KX175 front end, this has gold finished wheel and disk brake, however the forks are very long and would need to be machined down in length.

The DT250 has similar forks to the XT and is the nearest Yamaha equivalent.However the DT has two designs of forks, one with the wheel shaft in front of the fork leg like the XT and one with the shaft in line with the fork leg. Try to find the ‘in front type’. The DT has 36mm chrome tubes as opposed to the XT 35mm tubes, so you need to replace the yokes set as well, however this bolt straight in. However the DT clock bracket is not the same as the XT nor is the ignition switch.Once you have the 36mm yokes set fitted then you can either fit DT125LC forks, DT250 forks or XT350 Forks, which now allows you the choice of drum or disk front brake.


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FIGURE 7. THE FRONT FORKES.


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FRONT FORKS PARTS LIST

Ref Part No. Description Quan1 ¢3Y-12310-00-00 ENTIRE ASSY 12 3Y1-23136-00-98 TUBE, OUTER 2 13 3Y1-23126-00-98 TUBE, OUTER 1 14 4A1-23156-00-00 CLIP, OIL SEAL 25 1T3-23145-00-00 OIL SEAL 26 3Y1-23110-00-00 INNER TUBE 1 27 3Y1-23170-00-00 CYLINDER, FRTFRK 28 1W1-23173-L0-00 SPINDLE, TAPER 29 3J2-23114-00-00 GASKET 210 3Y3-23340-30-33 111 3Y1-23141-00-00 SPRING, FRONT FORK 212 583-23142-00-00 SEAT, SPRING UPPER 213 2W6-23118-00-00 SPACER 214 509-23158-L0-00 GASKET 215 122-23129-00-00 GASKET, DRAIN PLUG 216 3Y1-23191-00-00 BOOT, FRONT FORK 217 341-92090-60-00 BAND, BOOT 218 3J2-23183-00-00 CIRCLIP 219 3Y1-23111-00-00 BOLT, CAP 220 3Y1-23168-00-00 CAP, FRONT FORK 221 3Y1-2331E-00-00 GUIDE, CABLE 122 2NX-23356-00-00 BOLT 2 223 278-23181-50-00 BOLT, HEXAGON SOCKET HEAD 224 98580-06012-00 SCREW, PAN HEAD 125 92995-06100-00 WASHER, SPRING 126 509-23194-L0-00 SCREW, BOOT BAND 227 98580-04008-00 SCREW, PAN HEAD 228 92901-12100-00 WASHER, SPRING 229 3Y1-23317-00-00 HOLDER, CABLE 130 1W1-23389-00-00 GUIDE, CABLE 1


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IF YOU WANT A BIT MORE GROUND CLEARANCE.

On the large rear shock is an adjuster with a lock nut, use a ‘C spanner’ if you have one or a large screwdriver and a hammer if you dont and loosen the lock nut and then the main nut.Do up the nuts as far as you can i.e. allow the spring to be compressed by the maximum amount. then tighten up the lock nut. This may increase the seat height by 1 inch

REPOSITION OF THE TOP ANCHOR HOLE FOR THE REAR SHOCK.You will need a large bolt of say 12 to 13mm diameter and long enough to bridge the frame plates say 5 inches. plus some washers or spacers.

Remove the Battery, seat and tank.Support the bike on a stand.Remove bolt bolts that attach the rear shock.Mark the frame and drill a small pilot hole approx. 1.5 inches down the frame, its important to have the centre of the hole as low in the frame as you can manage.

General rule of thumb. For a bolt hole to work its has to be surrounded by metal of at least half the diameter of the bolt.Keep putting larger drills though until your large bolt will fit.Put spacers or washers in place to keep the eye of the rear shock central and fit the bolt.

If you have not greased the swinging arm bearings now is a good time to do it. do this every 12 months.NOTE. dont be fooled ...it is not sufficient just to remove the swinging arm bolt grease it up an put it back this is only half the job.Remove the chain, remove the swinging arm bolt. withdraw the swinging arm.One at a time Try to push out the steel sleeve form the fibre bush, and liberally coat this with grease and put it back, do the same with the other side.If you cant push these out then you are looking at 3 to 5 hours work to withdraw the fibre bushes and replace them. and £20 of parts.

Rebuild the bike.You will now notice that the lower rear shock pin will fit as it does not now align with the frame.You should now have say 1 inch more ground clearance and a inch higher seat height.


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IF YOU WANT A BIT LESS GROUND CLEARANCE.

That is you want the seat a little nearer the ground.On the large rear shock is an adjuster with a lock nut, use a ‘C spanner’ if you have one or a large screwdriver and a hammer if you dont and loosen the lock nut and then the main nut.Undo the nuts as far as you can i.e. allow the spring to be compressed by the minimum amount, then tighten up the lock nut. This may reduce the seat height by 1 inch.

Support the bike on blocks and loosen all 4 pinch bolts on the yokes that pinch the yokes to the fork legs, some very large screwdrivers will come in handy here. Using 2 screwdrivers in the yoke slot to make a small gap, slide the fork tube upwards say 15mm, pinch up the bolts and do the same to the second fork leg.

If you still want to reduce the set height. then have a look at the rear tyre, the standard size is a 17 inch tyre but most bikes have now been fitted with a 18 inch wheel and tyre. You can also fit the rear wheel off a SR250, this will bolt straight in and has a 16 inch wheel and tyre.

If you still want to reduce the set height, then either modify the seat by removing foam and have it recovered, an expensive option at £100 plus.Or fit a seat from a TT600, this will fit quite easily, as the 2 holes that bolt the TT600 seat onto the frame of the TT600 almost line up with 2 holes in the XT250 frame. with a little work and 2 washers you can bolt it on. This seat is quite thin and should reduce the seat height by 2 inches.

If you still want to reduce the set height, then fit a smaller front wheel also, a SR250 can be made to fit after a few hours of work.

If you still want to reduce the set height, then buy the XT225 Serrow model.


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XT250 SPECIFICATIONS.

XT250 SPECIFICATIONS.Initial frame no. 3Y1-00101Basic colours White and redFuel type Regular 8lt 2.1 gal/ 1.7lt 0.5 galDry vehicle weight 113kg, 249 lbs

Engine type 4 stroke sohc air cooled singleBore/ stroke/size 75mm/ 56.5mm/ 249ccCompression ratio 9.2:1Piston skirt clearance 0.035 to 0.065mm/ max 0.1mmRing end gap top/2nd/3rd 0.2 to 0.4mm/ 0.2 to0.4mm/ 0.3 to 0.9mmValve clearances cold, intake/ exhaust

0.06mm/0.15mm. 2th/ 6th

Oiling system wet sumpOil capacity dry 1600ccOil and filter change 1300ccOil type 20W40Carburettor Mikuni VM28SS/ 3Y1Main jet/ Pilot jet 165/17.5needle jet/ jet needle position 0.8/ 5DM65 FIXEDSlide cutaway or throttle valve 2.5 (30)Float level/ fuel level 23.5 +/-0.5mm / 3 to 5mmIdle RPM 1200 RPM

SUSPENSIONFront forks oil type/ oil level 10 Wt fork oil. 485mm 270ccSpring Length 456mmRear Monoshock gas pressure 15kg/cm 213 PSIMinimum Brake lining thickness 2mmFront tyre size/ pressure 3 by 21 inches 18 PSIRear tyre size/ pressure 4.8 by 17 inches 21 PSI

Transmission see engine oilPrimary drive type/teeth/ratio Spur gear/ 72-23/ 3.130Drive Chain 520 type 98 to 100 linksClutch friction plate thickness 2.8 to 2.5 mmClutch spring length 34.6 to 33.6mm

Charging System Flywheel magneto/ single phase/ half wave

Battery model/spec gravity/ charge rates

Nippon Denchi 6N6-3B-1 (6V6AH)/1.26/0.6A

Maximum Output 7.6v @ 2.0 A@ 8000 rpmCharge coil colour code/res Green and Black/ 0.34 ohms +/- 10%

IGNITION SYSTEM Capacitor Discharge IgnitionIgnition Timing 7 Degrees BTDC @ 1200rpm

Advanced to 32 degrees +/-3 degrees @


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4000rpmSpark Plug type NKG BP-7ES or Nippon Denso W22EPSpark plug gap/ torque/ cap ohms

0.7 to 0.8mm/ 2m-kg/10k ohm +/-20%

Ignition coil test gap/ prim res/ sec res

6mm / 1.0 ohm +/-15% /5k9 +/-10%

Pulser coil or pick up coil colour / ohms

Grey~Red &White~green/ 215 ohms +/-10%

Source Coil colour/ ohms Brown~Red/ 490 ohms +/-10%

LIGHTING SYSTEMHeadlight/ taillight/ winkers 6V 35-35W/ 6V 25-5.3W/ 6V 17WLighting coil colours/ res Yellow~Black/ 0.21 ohm +/-10%

TORQUE VALUESFront axle nut 14 * 1.5: 8.3~13 m-kgRear axle nut 16 * 1.5: 8.3~13 m-kgClutch Nut 20 *1.0: 7.0 m-kgDrain Plug 4081.5: 3.2 m-kgCylinder head cover 6 *1.0: 1.0 m-kgCylinder head 10*1.25: 3.8 m-kg

8*1.25: 2.0 m-kgEngine bolts 8*1.25: 3.2 m-kg


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HEAD Problems.If you have an oil leak.

The two round covers on the front and back of the engine are the tappet covers, and the large round cover on the side of the head covers the large cam shaft gear. Changing the rubber O rings on these is very easy. Just take of each cover prise out the old O ring, check for burrs with your finger on the cover and the engine, file off any burrs making sure no swarf gets into the engine, apply some grease to the slot and fit the new o ring, then refit the cover. This is very easy takes 5 mins per cover.I have only seen leaks form the large cam shaft gear cover, which was a result of burrs on the head, presumably caused by spanners when the engine is being worked on.

HEAD GASKET Change.

If the head gasket is leaking very badly, then that’s a longer job, say 2 hours.Remove the seat and the tank and the exhaust and the battery. Take the plug out, take all three covers off the head. Take the engine plastic left hand cover off to show the alternator magnet. Position the engine a top dead centre, its marked on the magnet with a pip on the engine case. Check this by, both tappets now have a few thou of slack, the piston is at the top of the stroke, and the large gear cog on the camshaft has a line going straight up. If the tappets are not slack then rotate the crankshaft one revolution, then it will be correct.

Remove the top engine mount, the ignition coil, the carb and the exhaust.Undo the cam bolt which holds the large cog on, undo the cam chain tension bolt and remove the tensioner. Use a piece of wire to support the cam chain.Undo the four head bolts and the two Allen key jobs. Now is the tricky bit try to lift out all 6 bolts. This may not be easy as one of the long 4 engine bolts just hits the frame. If you can’t lift out the bolts, loosen all the engine bolts and let the engine drop half an inch. Not forgetting the swing arm bolt and the small bracket behind the swing arm.

Lift off the head and replace the head gasket and the rubber O ring item 10 on figure 6.Put the head back on and put everything back together. Do up the 6 head bolts to a reasonable figure, then bolt the engine back in to the frame. Bolt on the cam shaft gear, making sure the line on the gear is vertical, and the engine is in the correct place, refit the cam chain tensioner. The steel pin should be flush with the large nut. Now you can rotate the engine carefully. If the cam chain gear does not line up exactly then you could easily have the cog one tooth out, remove the cam chain tensioner, remove the cog and slip the chain one tooth, put it all back and check. If it looks good, then turn the engine over with a spanner on the crankshaft and it should suck and blow and recheck the cam chain timing.Now with the engine bolted back into the frame, lean on the 4 head bolts in diagonal order and the 2 Allen key bolts, put the 3 head covers back on. Tighten up the cam chain tensioner. Bolt the carb, the exhaust, the tank, the battery and seat back on. Connect up the fuel pipe. Refit fit the plug. Kick it over it should have good compression.

NOTE: the Oil leak was probably due to a perished or ill fitting O ring ‘ its the size of a hula hoop’ make sure the new one fits well, if in doubt visit you Yamaha dealer and get a new one. The head gasket set for the XT250 is the same for the SR250.


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THE 12 VOLT CONVERSION.

XT250 DIAGNOSTICS.

WHEN THINGS GO WRONG ENGINE WONT START.

Check for a spark at the plug. Remove the spark plug cap from the plug and remove the plug from the head, use a car jump lead ensure the sparking plug body is grounded to the engine or the frame. Turn the key on and press the starter or kick over the bike, a large blue spark should result jumping from the plug pin to the outer. On a bright summer day this may be difficult to see. Note. It is important that you use a jump lead or wire, as you can damage the coil and CDI without a correct discharge path. Not to mention get a nasty shock.

In desperation if you are miles from home and you have a few tools on you, then you need to find out if there is 12 volts on the red and white wires, this signal powers the CDI, the coil. Its fed power via the kill switch power from a relay mounted near the battery. Use a winker lamp as a tester and look for 12 volts on this wire. i.e. remove the winker lamp wire from inside the headlamp and touch it to the red and white wire in the kill switch area, if it does not light you have no power on the CDI. You can jump power from a brown wire, one goes to the horn, pull it off the horn and connect it to the red and white wire, turn the engine over and look for a spark. If it sparks then drive it home.

If the battery is poor or not charging, then turning the starter motor over will consume a lot of power not leaving much left to power the CDI, put the bike in third gear and push it down the road. With the engine running check the battery voltage it should read 13.2 volts. If not check the leads to the rectifier. The output path is red to live battery and brown to switched power it needs both. And both white leads are ac from the alternator. If all looks good you may need a new rectifier block.

The most likely failure was the relay which powers the CDI, it’s located near the battery, its fed power and is activated by the neutral switch. Its task is to power the CDI and to remove power when the ignition switch or the kill switch is operated. If this fails then you can un plug it make up a jump lead with two spade connectors and a few cms of wire and joint the two sockets together that are coloured ‘red and white’. This will get you home but removes the protection i.e. if you are in gear and the clutch is not pulled in the starter will try to drive the bike away.

The kill switch have been known to fail, open them up and have a look, perhaps a wire has fallen off or one of the tiny screws has come lose and the tag is no longer connected to the switch.


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If you have the XT250 with the 12 volt conversion, you will need this diagram.


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FRONT WHEEL1 3Y1-25111-00-98 HUB, FRONT . . . . . . . . . . . . . . 1 LOW GLOSS BLK2 90560-15293-00 SPACER . . . . . . . . . . . . . . . . . 13 146-25116-00-00 FLANGE, SPACER 2 . . . . . . . . 14 93306-20226-00 BEARING . . . . . . . . . . . . . . . . . 15 93306-20209-00 BEARING (B6202) . . . . . . . . . . 16 93102-20009-00 OIL SEAL . . . . . . . . . . . . . . . . . 17 3Y1-25121-01-98 . PLATE, BRAKE SHOE . . . . . . 13Y6-2533A-01-00 . PLATE, INDICATOR . . . . . . . . 13Y6-25351-00-00 . CAMSHAFT . . . . . . . . . . . . . . 199999-01734-00 BRAKE SHOE PLT ASSEMBLY 1 LOW GLOSS BLK8 90480-10068-00 . GROMMET . . . . . . . . . . . . . . . 19 93105-47007-00 OIL SEAL . . . . . . . . . . . . . . . . . 110 25G-W2536-01-00 BRAKE SHOE SET . . . . . . . . . 211 90506-17328-00 SPRING, TENSION . . . . . . . . . . 212 308-25135-00-00 GEAR, DRIVE . . . . . . . . . . . . . 113 214-25149-01-00 CLUTCH, METER . . . . . . . . . . . 114 90201-22283-00 WASHER, PLATE . . . . . . . . . . . 215 93410-22014-00 CIRCLIP, S-TYPE . . . . . . . . . . . 116 308-25138-00-00 GEAR, METER . . . . . . . . . . . . . 117 90201-07076-00 WASHER, PLATE . . . . . . . . . . . 118 109-25136-00-00 BUSH . . . . . . . . . . . . . . . . . . . . 119 93104-07003-00 OIL SEAL . . . . . . . . . . . . . . . . . 120 3Y6-25351-00-00 CAMSHAFT . . . . . . . . . . . . . . . 121 3Y1-25155-00-00 LEVER, CAMSHAFT 1 . . . . . . . 122 90101-06278-00 BOLT . . . . . . . . . . . . . . . . . . . . 123 95380-06600-00 NUT . . . . . . . . . . . . . . . . . . . . . 124 94416-21326-00 RIM 1.60X 1 . . . . . . . . . . . . . . . 125 90480-10068-00 GROMMET . . . . . . . . . . . . . . . . 126 3Y1-25104-00-00 SPOKE SET, FRONT . . . . . . . . 127 94130-21416-00 300X21BS TW11 4PLY . . . . . . . 128 94227-21123-00 TUBE (2.75-21) . . . . . . . . . . . . . 129 94330-21084-00 BAND, RIM (3.00-21) . . . . . . . . 130 403-25381-01-00 AXLE, WHEEL . . . . . . . . . . . . . 131 90387-15600-00 COLLAR . . . . . . . . . . . . . . . . . 132 322-25118-00-00 COVER, HUB DUST . . . . . . . . . 133 90171-14020-00 NUT, CASTLE . . . . . . . . . . . . . 134 91401-30030-00 PIN, COTTER . . . . . . . . . . . . . . 135 90201-15785-00 WASHER, PLATE . . . . . . . . . . . 2


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repair xt250 yamaha 1980- 1983

Documents

bright summer day

xt225 serrow model

rear shock absorber

top dead centre

local yamaha dealer

cam chain tensioner

pan head screw

swing arm bearings