Dieseling during shutdown is caused by an idle speed that's too high. Adjust the carburetor correctly and the problem will go away. Mixture and/or ignition timing has very little to do with the problem. If it won't idle somewhere around 500 RPM, fix the carburetor or find the vacuum leak.
Jerry


"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!