I was using Redline's article - IDF Carburetors Low Speed Circruit Turing.

The engine runs pretty well with the idle jet on #2 fully closed. I went down one size, no change. There are no vacuum leaks.

Any gurus have any ideas.

Thanks,

If the idle mixture adjustment screw has no effect, or can be closed all the way, there are three things that come to mind.

1. The idle jet is clogged and isn't allowing fuel to pass, so the screw has no effect.
2. The venturi is too small and the engine is creating enough vacuum at idle to engage the main jets.
3. The ignition system for that cylinder isn't working correctly and cutting fuel back doesn't have an effect because the spark plug isn't firing correctly anyway.

it could be idle jet or the idle circuit. remove the idle jet, don't loose the o-ring behind the jet holder, and blow it out from the orifice backwards toward the holder end. blow it out on a paper towel and see if there's any specks on the towel. a can of compressed air works great for this. the trouble shooting guide in the CB weber manual lists 7 potential causes for a non-responding idle/air mixture screw. you should get a manual.

k

A couple more:

A vacuum leak and your not pulling air through the idle circuit.
Float level too high and your spilling/pulling fuel over from the mains
Butterflies open too far at idle and your pulling fuel from the progression ports.

If I was a betting man I'd go with Mark's first description.

Thanks for the replies: I have something to do this weekend.

No vacuum leak
Jet is not plugged, but there may be crud elsewhere in the circuit
vents are 32, about as big as you can get
Igntion - maybe
Float too high - just adjusted but worth another look -- 10 mm and 32 mm??
Butterflies open too much - all are the same.
Manual - on order.

That's 10mm with the gasket. I usually set mine at 11mm.

Air screw, if set to far out the smaller air bypass screw will be out of range.