Ed: I an using a 4 cycle Super plug from Horizon. For what its worth...One of the last runs on my Homelite 25cc engine (on test stand) I covered the front top portion of cyl with tin foil. It helped. I have a heat sensing gun to read temps. It would be neat to have a air inlet controlled by a temp sensor to keep engines running at a desired level. Some air cooled Auto engines did have this feature. I guess you can see a water cooled engine would run at a more even temp. Too Heavy for aircraft...darn. Thanks Capt,n