[Bruce Edwards]

Ok beg to differ on this one. If the fuel mix at idle is to lean it will cause run on. In the 70's with the new laws the factory cars all came with anti diesel sol's to control the run on problem brought on by the leaner mix that the new law created. The sol was the idle set not the screw on the carb and the priomary was set to shut all fuel or most fuel of at shut down. Lets not forget that at this time the compression was dropped as the fuel was changed from leaded to unleaded.
Run on can be caused by a few things. Granted one is to high compression with poor fuel however in this case it is reported as a new problem. Thus something has changed.
The trick is figuring that out. For me, after working on cars of all kinds for over 35 years, I find cabs and or spark to be the biggest factor. I have built engines with compression in the 12's on pump fuel with no run on or ping. All a matter of setting it all up so everything works together.