ORIGINAL: opjose

Eventually he resorted to filing a small 2mm "half moon" on the throttle barrel opening at the point of smallest closure.

This increases the airflow at idle permitting a leaner low speed idle mixture.

I had an extra ST carb laying around, purchased in my attempts to cure the problems... so I tried the same thing with the ST carb.

Sure enough it fixed the problem PERFECTLY.

I've done this to two similiarly affected engines with equal success each time.