Re: small engines

Posted by jdemaris on April 25, 2005 at 19:57:34 from (209.23.30.201):

In Reply to: Re: small engines posted by msb on April 25, 2005 at 14:42:06:

Don't know if he's got a Walbro, Tecumseh carb, Briggs, Carter, or whatever - but just want to add one thing to what you said. The low speed idle mixture screw also serves as the "accelerator mixture" screw - same purpose as an accelerator pump on an automotive carburetor. So, it should be set initially to let the engine idle at it's best speed when warm (not hot). But then, you try reving the engine up - from low idle to high speed - just like stomping on the gas pedal of a car. If it hesitates and leans out, it has to be opened a bit. So, it's actually to be set with a compromise between best idle and best acceleration. Regardless, it should still wind up 3/4 - 1 1/2 turns as you mentioned.
Also - sounds silly but I've seen it happen several times. If the carb is an older Walbro - you can't adjust the idle-mixture screw with the carb. upside down. What happens is - sometimes the carb. gets taken off to clean - and then gets held upside down during assembly. With the Walbro, there is a floating idle jet tube inside the carb idle circuit - and if you screw in the idle screw while upside down - it will smash the tube and ruin the carb.

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