- Wed Apr 29, 2015 10:50 am
#47210
Girish writes: "When you say air screw is running too weak you mean too lean or too rich. I assume at just 1/4-1/2 turn out, it is running too rich. no?"
I don't think I said the "air screw is running too weak", but it's my fault for not explaining myself very well.
As you know, unscrewing the air screw increases the amount of air going to the engine at idle, without increasing the amount of fuel. Thus it makes the mixture "weaker" or "leaner" (both terms are commonly used and mean the same thing).
As a general rule the air screw would typically be 1 - 2 turns out if the correct idle jet was installed and everything else was working OK. The fact that yours must be turned much further in suggests that something is making the mixture too weak/lean and you are having to compensate by turning the air screw further in than normal.
That is what gave Frank the clue, I think, that there might be an air leak somewhere. The vacuum inside the inlet manifold will draw air in through any leaks, making the mixture reaching the combustion chamber leaner than it should be. At the moment you are compensating by moving the air screw to a richer position than normal, but as you know it doesn't work very well.
I suspect that once you've fixed the air leak the idle will be much more stable, and you will find that the air screw must be wound out somewhat further to get the mixture right.
I don't think I said the "air screw is running too weak", but it's my fault for not explaining myself very well.
As you know, unscrewing the air screw increases the amount of air going to the engine at idle, without increasing the amount of fuel. Thus it makes the mixture "weaker" or "leaner" (both terms are commonly used and mean the same thing).
As a general rule the air screw would typically be 1 - 2 turns out if the correct idle jet was installed and everything else was working OK. The fact that yours must be turned much further in suggests that something is making the mixture too weak/lean and you are having to compensate by turning the air screw further in than normal.
That is what gave Frank the clue, I think, that there might be an air leak somewhere. The vacuum inside the inlet manifold will draw air in through any leaks, making the mixture reaching the combustion chamber leaner than it should be. At the moment you are compensating by moving the air screw to a richer position than normal, but as you know it doesn't work very well.
I suspect that once you've fixed the air leak the idle will be much more stable, and you will find that the air screw must be wound out somewhat further to get the mixture right.