Originally Posted by Legend Racer

whats the difference if i set it at 3000rpm or 5000rpm, and then start doing the tuning?

Originally Posted by jonahmano

And Here are the other two versions, bit similar but I did understand you meant only by reading the other two which I am pasting below.........

Version 1

Dear Biker,
Are you tired of cold starts? Need to raise the throttle everyday to get the cold engine running?
Does someone have the same bike as yours and are you tired of losing to him in drag races?
Suddenly, the fuel efficiency has reduced after a service?
Has the mechanic has screwed up your tuning?
Engine gives hiccups when you open the throttle?
Or your bike is just missing that smooth acceleration whenever you want?
Or your engine overheats even if you did not race too much.

May be the following will help you in tuning your mean machine for optimal power delivery and best fuel economy. This guide aims at tuning the fuel/air screw to give you an optimal air-fuel mixture. An optimal mixture gets maximum performance from your machine.
Getting The Basics

I am assuming that you know driving very well and have completed at least 1000kms on road. If not, then you are too amateur to read this guide.

Every bike has a engine (motor/mill/muscle) and a carburetor (breathing system/heart) – Yeah I know that. My point is, I assume that your engine is in perfect condition. That is, there is no oil leaking from it etc etc.. The next assumption is that your engine is not DEAD. You know where your engine is and where your carb is and you have a screw driver/blunt knife with you. Your machine must have finished at least one service ~500kms or more. Also make sure you do not change the fuel type while tuning i.e. Power, Speed, Extra premium, normal unleaded etc.
This Guide Applies To

All the single cylinder bikes, 2 stroke or 4 stroke having a carburetor. Tachometer is very handy and a must for a newbie or the tuning process will be very slow or painful or imperfect.

Disclaimer: Though whatever I have written here wont do any damage to your machine, finally you must not blame me for whatever happens. I am here to help if anything goes wrong.
So Lets Get Started

Warm the engine nicely. Go get a ride around the town. Speed nicely at least upto half the top speed of the bike. Drive at least for 10-15 minutes so the engine system warms up nicely or you’ll get a bad tune. Do not just leave the engine idle and start with process. I mean it. Ride the bike.

Now that the engine is adequately heated up, you are ready to begin with the process. You can select a place far away from the city or your residential area so that you do not disturb the tired, sick, disgusted, old people or babes (babies) living in your colony. You are likely to be shooed away from them when you are at a critical point. You may choose a place near your girl friend’s house just to impress her! Put the bike in main stand and get hold of your screw driver. That is all you need, together with your eyes, brains and ears.

Searching the fuel/air screw… The above mentioned screws are responsible to adjust the air-fuel ratio which forms ‘food substance’ for your engine. You can relate it to our human body, where proteins, carbs, fats, water etc all are required in appropriate proportions with respect to each other for good strong body.

There is another screw which sets the idle speed of the machine. This screw is not related to pickup or mileage. It just sets the engine rpm at ’’idle’’ run. 2stroke machines have an Air screw and 4 stroke machines have a Fuel screw. I hope you note this VERY well. Air screw is located on the carb away from the engine. [ Engine - Carburettor - Air screw]

Fuel screw is located on the carb but its near the engine. [Engine - Fuel screw - Carburetor]. If the make of your carb is Mikuni (Pulsar, Yamaha, Fiero) the fuel/air screw probably will be of brass (golden colour). If you fully unscrew this screw and take it on your hand, you will see a needle like tip.

Idle screw is closely linked with the throttle cable. Idle screw can be turned by the hand. Screw driver is not essential for it. Finding these screws are very simple. If you still cannot find the air/fuel screw, ask your mechanic or I can help.

Ok now what? Apart from the above difference I gave between Air and Fuel screw, there is one more major difference. Fuel screw turned in (clockwise) gives a lean mixture and turned out (anti-clockwise) gives a rich mixture. Air screw turned in gives a rich mixture and turned out (anti-clockwise) gives a lean mixture. Lean means more air, less fuel. Rich means more fuel, less air. This ends the basics.
Getting Things In Action

Turn the idle settings screw so that rpm reaches about 3000 rpm. Now tune the air/fuel screw to make the mixture leanest as possible. Please refer to the above whether you must turn the screw clockwise or anti clockwise.

As you make the mixture leaner, slowly the engine RPM decreases… Go on doing this until you have put the fuel screw to the leanest possible point. At the same time, ensure that the engine does not stall, by turning the idle-screw.

Tough huh? You’ll get used to it

OK the engine is running and the mixture is lean. If you notice from the engine sound OR if you see the tachometer, the engine RPM will not be steady at this point. Now very slowly start turning the fuel screw anti-clockwise, quarter to 1/8th turn at a time. You will notice that the RPM increases slowly and steadily. Again, do this very very slowly. Also count the total number of turns as you wind out the screw.

You’ll notice that when you have turned it to about 3-4 full revolutions, the engine RPM slowly becomes constant. It is this point that you must stop screwing more. This probably is the optimal setting for your engine.

Further on, try turning the screw even more and more to 5-7 revolutions and you’ll notice that the engine RPM will slowly decrease. When this happens, you are just putting in a too rich mixture in your engine. At this point the engine loses all the fuel efficiency and the mixture is not optimal. Repeat the process about 2-3 times. Count the revolutions each time and get the setting which you feel is correct.

OK the engine is humming perfectly, now what? Decrease the idle setting screw to about 1000rpm in the tachometer. When the engine slows down, just twist the throttle. The response should be crisp and quick. It should not give any hiccups! Try shutting off the engine and restarting. The engine MUST start in a single kick or self with out giving throttle. If this happens, the setting is ok. Now get a ride and you’ll notice the difference for good or bad

You’ll immediately notice change in the engine sound and the throttle response. Your engine can become more smooth or harsh. Another important point is, Ride and Feel. Always take a ride and get the feel of the bike in each gears, check the response and the engine sound. You’ll quickly come to know once you get the feel of the bike that you want to make the mixture rich or lean.

It may take a few iterations before you fix a setting as permanent. Try calculating the mileage per liter and tally it with your setting and the feeling you get.


Troubleshooting



Here are some symptoms and their quick solutions:
Engine dies while tuning.
Try the process all over again. This time set the idle screw higher/faster.
Engine gives hiccups while driving, specially while in higher gears.
May be the mixture is too lean. Try again.
Engine heats up.
The mixture is too lean or too rich. Try again.
Whenever I race up the engine, the rpm increases fast but very slowly comes down to idle.
The mixture is not optimal, probably towards leaner side. Try again.
Too much low end torque and the engine sound is very beaty/thumpy.
You’ll face a low mileage surely, when you drive below 40kmphr. You have tuned on the higher/richer side.




Version 2


BASIC GUIDE FOR CLEANING & TUNING A CV CARBURETOR.
REMOVING THE CARB:
Remove all cables from carb body. (Accelerator & Choke)Remove the Fuel supply. (Be sure that the fuel cock is in off position)Now using a (-) screwdriver unscrew the two ring clips on both side (Engine side & Air box Side)of the carb. Now u will be able to remove the carb form the manifold.
CLEANING THE CARB:
Open two screws on the lower side of the carb. The lower part should now open. Clean all the parts inside using fresh petrol or some carb cleaning liquid. Be careful about the small parts. I will suggest to take a snap of the inside by your mobile cam before cleaning. it will help you to reassemble the carb again. If you can clean the both jets using some still wire (Say Clutch cable wire), or go to petrol pump for air pressure gun. These will clean the jets properly. Now using the snap assembled the CARB properly.Dont forget to keep the rubber washer it its place.Use the same way to install the carb into manifold. Check for all screws, pipes, fuel pipes etc. If possible replaced or clean the Air filter element before you jump to the tuning process. You will able to find the procedure to replace or cleaning of the same in your user manual.
TUNING:
Now for tuning find out two screws in the left side of the carb body, one is AIR screw and another is IDLE screw. AIR screw is small and should be in the left side of the carb. IDLE screw is little big and it comes with a spring to support it. Before you start the tuning, it is good practice to warm up the engine for a while, say 5 minutes, to reach it in its operating temperature. Now turn the IDLE screw and you will see the rpm is increasing, now by turning the screw fix the rpm at around 5000 rpm. Now this is the tricky part, using a small screw driver turn the AIR screw clockwise, you will see the rpm will now decrease, turn it fully in its position, don’t try too hard, it can damage the screw. Now the rpm will come down and engine will spatter. Turn the screw anticlockwise to that position where the rpm will not increasing no more, for that you have to turn the AIR screw 3- 4 times around. Now turn the IDLE screw, the rpm will fall, fix the rpm at around 1200-1300.Now take a spin, say 5 km to warm up the engine. Check if the idle rpm is increasing; adjust the IDLE screw again to fix it in 1200-1300 rpm.And you are done.

** THIS IS THE BASIC THEORY FOR TUNING THE CARB. YOU CANT ACHIVE THE GOAL AT FIRST HIT, BUT TRY IT YOURSELF, THIS IS NOT A ROCKET SCIENCE. I DID IN MY Bike ALSO; IT TAKES FIVE – SIX TIMES TO GET OPTIMUM POWER AND PICKUP.

Originally Posted by Legend Racer

whats the difference if i set it at 3000rpm or 5000rpm, and then start doing the tuning?

Originally Posted by road_ripper

I keep it at 4000 rpm and tune the bike.. the result is good of both the worlds, I get mileage of 43-45 with superb acceleration on my 180 ug3.
When i had tuned the bike keeping at 3000 rpm, the mileage was 45+ but pickup was not that brisk, So I guess lesser rpm will tune it for mileage and higher rpm will tune your bike for power...

Originally Posted by Yasir Qaiyum

Hi guys!! I read this thread in morning and decided to tune by bike(pulsar150UG4).. the problem is I couldnt find any screw except the one which is in golden color... It is on the left side of carb.. which screw is that? And where is the other screw (air screw or fuel screw)....PLEASE HELP...

Originally Posted by Yasir Qaiyum

Hi guys!! I read this thread in morning and decided to tune by bike(pulsar150UG4).. the problem is I couldnt find any screw except the one which is in golden color... It is on the left side of carb.. which screw is that? And where is the other screw (air screw or fuel screw)....PLEASE HELP...

Originally Posted by road_ripper

Please mention the link and give coutesy to the writer after the copy paste job is done...
The source of this review is given below
GENERAL ADVICE ON BIKES Review, GENERAL ADVICE ON BIKES Price, GENERAL ADVICE ON BIKES Mileage, Tuning your carburettor for optimal performance & - MouthShut.com

Originally Posted by Legend Racer

easy dude..u can find with patience...sit on the left side.u found out the idle screw..nice..now just to the left of that on carb.its a small one.just note that ur screw driver meets this screw in perpendicular.i mean if u turn thz clockwise thz goes inside the carb and vice versa..hope thz wud b easy to find.take care u should not fiddle with thz screw simply..take care.its properly instructed in thread.i did mine P150 UG2 @ 3000 rpm..i did for my frd @ 4000rpm..thr is difference in pick up.i ve posted my doubt in this.i mean till wat rpm u can get utmost acceleration jst by thz tuning.

Originally Posted by abhisheklakhanpal

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 , it’s 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

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
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) or maybe 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.





Towards biking Independence......

Cheers!