I have my dwell set at 29,ranges slightly between 28.7 and 29.4.Idle mixture screws are 4 turns out,and idle speed is 850 and steady.When i rev the engine,the dwell reading decreases so the mcs is putting more fuel in?.So more dwell is leaner and less is richer,is this right?.Also is the dwell supposed to range
up and down very much,mine at idle stays pretty much on 29,unless i rev it.
Last question,if the plug that covers the lean stop screw,is'nt there,can it vibrate out of adjustment.

Alicat.

 

The stock cover over the IAB screw is just there to prevent tampering, not to hold it in place. The screw has 2 o-rings on it further down that effectively hold it in place so it can't vibrate out of adjustment (that's not really their primary job, but that's what they do).

Dwell can and does change under various running conditions. No carb is going to give a perfect A/F ratio under all conditions so the ECM must constantly stay on top of things via the O2 to trim the mix. And a "snap throttle" test is a very big change in operating conditions in a very short period of time- there may even be special programming in the chip to temporarily ignore the O2 and do a certain set of changes to the dwell for a short period of time for all I know.

Actual running conditions on the road are the best for determining if things are set reasonably close (dwells within reasonable ranges). Blipping the throttle in the driveway or just revving it up under no load bears little resemblance to what is going on while driving out on the road.

 

The lean stop screw has enough tension from the spring underneath it to keep it in place usually, but with out that plug in place I would be concerned about debris entering the float bowl area, especially water if it rains. Or in your case sand and dust. The plug also would prevent excess fuel vapor from escaping the bowl area.

 

After looking at the carb diagram,i realised that i was looking at the rich stop screw.The lean stop screw still has the plug over it.I can put a plug of silicone on the one thats missing.

Alicat.