It could be you don't have a fuel delivery problem. Is the timing is a bit too far advanced or the idle speed a bit too high? I think the idle speed numbers on the under hood labels are a bit too high for the Weber carb. Also, dirty combustion chambers can cause dieseling. You could try filling it up with premium gas and put some fuel system cleaner in it. Take it for a good fast run on the interstate for an hour and clean out the combustion chambers. Before you shut it down check your idle speed and if necessary adjust it down to about 650 rpm for manual tranny. 750 for automatic.