Run it at idle with the choke open, warmed up. Look for spots of fuel evaporating on the closed throttle plate. This will indicate a leaking needle vavle in the float chamber, overfilling the chamber and leaking into the carb throat. This could be the source of your dieseling, too. You also should spray some water into the carb throat while holding a very high idle, using a misting spray from a plastic pump spray bottle. This will clean off any carbon deposits in the combustion chambers which cause white hot glowing spots that power the dieseling...

ANd get a 190 tstat...