Dear Hyper milers
I decided to put up this post after cruising the net to find out sites that explain fuel air mixture settings on normal carbs and did not find a satisfying answer.According to an old russian automobile repair book there are two screws with springs on them[which is true]in newer vehicles there are more,what we are interested in are two screws one located at the accelerator cable end and the other at the base of the carb . The one located at the accel site is for idle speed control and the one at the base is for fuel air mixture control according to the book[very true].
So what we do is slightly tighten the idle screw to make it idle faster and then what we do is tighten the air/fuel mixture screw in finger tight with a flat screw driver,if u are right then u will notice the idle getting low,if engine is trying to stop or idle gets shaky,tighten the idle screw some more to achieve a stable idle speed.Now u should unscrew the air/fuel mixture screw a quarter turn and then try accelarting if it is good leave it and then try driving if there is a popping sound from carb it means fuel ratio is too low so unscrew the air/fuel screw a bit more and try driving again if there is no popping sound but u notice a jerky or sluggish behaviour unscrew the said screw a bit more.
Before doing all this it is a good idea to remove one spark plug and look at the color of the tip,if it is black and sooty then it means the above procedure must be done,An ideal spark plug color is gray,dark gray,reddish for certain fuel kinds.
Advantages of doing above procedure
1.fuel savings
2.engine oil lasts longer[less carbon fouling]
3.some older engines have a tendency to foul spark plugs when there is too much fuel entering the system.[of course this might also be from other factors].But I have helped many a poor soul who was told they need to get their engine overhauled to stop spark plug fouling.[of course most spark plug fouling is from a tired engine]
4.More power and sport car like speed[funnily the inverse applies,more air+less fuel =good performance.]
5.u become eco friendly less pollution
6.cat converter will not get clogged up.
7.less oil burning.
Disadvantages of doing above procedure
1.sluggish performance in the morning or cold weater.
2.longer warm up time.
3.carb is sensitive to smallest dirt particle in fuel.
4.jittery idle.
5.might need choke for morning starting.
The other point I wrote this point is because I noticed that most mechanics here usually adjusted carb idle speed by unscrewing the air/fuel screw a lot imagine the poor soul who is gonna drive that car.
jarre
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