Seafoam is expensive, water works just as well. Just use 1/2 cup of water, a 1/4" vacuum hose, get the engine nice and warm, connect the hose to manifold vacuum and insert the other end into the water for one (1) second sips. It helps to have the rpm at about 2000. That will get rid of most of the carbon in the cylinders and should help your dieseling problem.

Remember, the vacuum will drain a full cup real fast! That much water will fill a cylinder and break a connecting rod or wrist pin.

Klaus
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My advice is free, so you got what you paid for...