carburator tunin carburator tuningg

8/11/2019 Carburator Tunin CARBURATOR TUNINGg

1/3

So ,

i figure most of us are still riving around carburetted bikes and at some point of time

, some dumb ass mechanic will screw it up for you (like a Bajaj Auth Service for me ) ,

or some drastic altitude changes will leave you feeling powerless. This goes to say ,

that your carburettor will be out of tune .

So , while i have kinda figured the trick , i m sure none of you wanna be slaves to

these headless mechanics waiting to tune a blunder for you .

A little Guide to tune you 4 stroke CV carburettor for the optimal ( Not power

oriented ) air fuel mixture.

There are mainly two screws used for the tunning of a carburetor

1.Fuel screw(4 stroke) or air screw (2 stroke)

2.Idle Rpm screw

The main difference between two stroke the fuel screw is that for the fuel

screw(used in pulsar etc) Clockwise tightening makes the mixture lean , and

anticlockwise loosening makes the mixture rich.

For two stroke bikes using an air screw the setting is exactly opposite.

The idle rpm screw is what sets the warm engine idle rpm . The greatest significance

of the idle rpm or pilot setting would crop up at the point that it affects 1/8th of the

initial throttle response. After that , its the butterflies and other that take over . But

this initial turning is critical so as to ensure a smooth pickup as well as control

knocking or over racing.

Judging the air-fuel mixture for the bike can only be done on a warmed up engine.

Warming up the engine


2/3

1.Drive for atleast 10-15minutes before trying to adjust any of the carburetor setting.

2.Especially for CV carburetors, used in the pulsar, use 1/2 throttle on an uphill for 1

minute. ( alternative )

Setting the mixture

1.Set the idle screw at 3000rpm

2.Now adjust the fuel screw for the leanest possible mix without stalling the engine.

3.Now after adjustment is made the rpm becomes constant

4.Now , adjust screw to tune within the lean range

5.Decrease idle rpm to about 1100

6.Check the throttle for a quick and crisp response. The crispiness is important

Also check for instant start

After warming and adjusting , drive for a while to check the spark plugs for the

following signs

1.White Deposits : Lean Mixture

2.Black deposits : Rich mixture

3.Sandy side of chocolate brown : Ideal mixture.

Please note that the fuel mixture is always checked by driving between 1/4 th and

3/4th of the total throttle twist. This also goes to imply that the throttle body must

have a uniform response to the same twist at all levels and is working perfectly.

The other , not so accurate way to check the correct mixture is the silencer or

exhaust fume . Place your hand at the exhaust as you rake the engine after 1/4th of

the throttle .

1.The sign of the optimal mix is that your hand feel slight warmish moisture as the

throttle is increased a bit . Then check the same sign at constant throttle.

2.The very heat or temperature of the fumes at the upper limit of the power band

should not feel too much to keep the hand there for about 10 seconds.

A few signs for your carburetor out of tunning


3/3

1.RPM rises fast but reduces slowly : Mixture is not optimal , usually on the leaner

side.

2.Grunting sound (too much torque) : Rich mixture.

3.Engine knocking at low rpm without power : Lean

4.Not enough power , overracing at high rpm for same speed : Clutch setting req .

Mix is a little lean

A Lean mixture is usally more harmful than a richer one . This is because , the engine

is knocking at a higher rate for the same power . Thus the high compression damages

the pistons causing holing(hole in the top center of the piston).It also jerks the entire

combustion chamber which may loosen the o-rings as well as cause uneven wear.

For this reason it is necessary that you always try to keep the needle in the

powerband for medium and overdrive gears, and also never try and keep the bike in

the same gear for thought of better efficiency.

For those of you who think that a richer mixture is a gateway for more power, it may

be noteworthy of a mention that even a richer mix is damaging and causes faster

wear and tear.

Hence engine life is reduced though it will function better than a len mixed

carburettor. In case performance is what you look at , Jetting of the carburettor is

the right way to go. It is basically increasing the fuel pipe radius as well as the air

pipe, to allow for a greater fuel flow rate. The most significant increase of jetting is

felt at the top end , where the limiting fuel flow is increased, thought a difference is

also felt throughout the entire RPM range.

However , once you drive a day or two , you will figure if your setting is correct or not

. If the mixture is the optimal one then just a single anticlockwise turn ( richer) ormaybe two will give you a reasonable boost in the power , though naturally you are

sacrificing the Fuel effiency , although it wont matter much . But , repeat , test the

optimal setting for atleast two days , before switching to the optimally rich setting .

Coz knowing what is right is the only way to know , know what is beyond right.

carburator tunin carburator tuningg

Documents