Basic idle setting ?

[welsh.Z.S.]

Changed my idle screw today from the crappy plastic one to the nice shiny easy adjustable one , is there a basic setting to go buy with the idle screw now so I can get a rough point to start from ? IE 1.5 turns out etc .. bike has a fresh top end etc so is nice and​ crisp

 

[motopsycho87]

I'd air screw you should start @ 1.5 turns out. Anything under 0.75 out and 2.5 out requires a different jet.

If it's less than 0.75 out you need a larger idle jet

If it's more than 2.5 out you should first check your needle. Most people find that the original needle allows fuel by at idle, if you've already got a better needle. Then smaller pilot.

Idle adjuster screw is adjusted to whatever gives the slowest but most stable idle. Some run with their idle slightly higher to avoid stupid stalls in slower sections (woods etc)

Make sure all adjustment are made at running temperature. You need to have ridden the bike, idling and revving for a few minutes isn't enough to uniformly heat the engine.

 

[TheLetterJ]

Whenever I've just rebuilt a carb (any carb) I turn the idle screw until you can just start to see daylight under the slide, and turn the air/fuel screw 1 1/2 turns out from seated, that's usually a good baseline to get the bike started. It is easier to fine tune the idle down from too high of an rpm, than it is to have to keep making adjustments and restarting the bike when trying to turn the idle up.

 

[Jakobi]

As above. Another method you can use is to listen. Back it right off until you head the slide stopping hard against the carb body. Then continue making small adjustments while letting the slide drop back down. You should hear when it makes contact against the idle screw. That's about the point it starts to lift.

 

[mjtursky]

The reason Keihin went to plastic for the idle speed screw is to avoid breaking the tab on the slide. This occurred when people would let the throttle snap back when revving the engine. I found the screw used on Polaris snowmobile Keihin carbs to work better. Bigger knob and slightly longer. Be sure to get the correct spring with the adjustment screw.