idle screw has no effect,, why?

[Nevada Sixx]

if a carb's idle screw has no effect, does that mean a pilot jet is too lean or too rich?
89yz125

 

[smb_racing]

the idle screw or the air screw? If it's the idle screw then it means your main is a bit rich, as the idle screw moves the slide up. The air screw controls the pilot jet, if turning it out does not increase the engine speed you're too rich on the pilot. Optimal for the idle screw is no more than half in and for the air screw is two turns out from all the way in. Hope this helps.

 

[250motoxer]

Let me get this right....smb_racing. The main has an effect on idle? Hmmm.... I thought the pilot worked idle to 1/4 throttle and the main only effected wide open throttle... Am I wrong?

 

[Glitch]

Nevada, is your bike idling too high or too low?

 

[bruce j]

Another thing that can make the air screw ineffective is an air leak somewhere in your intake system. You will probably notice other signs of the engine running lean if this is what's happening.

Forgive my ignorance here, but are you sure the pilot is too rich if turning it out doesn't increase idle speed? I would have thought the opposite would be true - that turning it out, and thereby increasing the amount of air in the pilot system, would help correct for a rich pilot jet and so increase idle speed. If I'm right, then the pilot is too lean or is plugged. Any comments from some jetting experts out there?

 

[Nevada Sixx]

my bike seems idled too low, and my idle screw doesnt have any effect.
I believe im supposed to turn it in to make it idle higher. My bike always seems to run rich,, stock calles for a 20/270/needle in second position.
I use a 15/260/needle in second. Before i got my enging ported for bottom end power,, my idle screw worked, and i used a 15/220/needle in second postion. after i got it ported, my engine ran lean, so went up to the 260 main. I also use a moose reed spacer if that helps.
But, im just not sure why my idle screw wont idle up and down anymore....??
thanks..

 

[smb_racing]

yes if the speed doesn't change by turning it out then you're too rich on the pilot, this being that the air/fuel mixture it so rich that the added air from turning out the air screw has no effect on the engine speed.

250motoxer, the main has an effect on idle to an extent, turning the idle screw in raises the slide which in turn raises the needle allowing the bike to "pull over" from the main jet slightly. This isn't the case on some MX bikes that have the idle adjustment on the choke knob however, I'm still not sure how those things work.