dirtybird, are you using the plug supplied with the tngine or one supplied by RCS ? If your using an Autolite replacement, the threads are cloce but not right. Found out the hard way. If you are usint the plugs supplied by RCS tighten that sucker down. I have three ZDZs 2-80s and a 100, never in 2 years hads a plug come loose. (except the Autolite I put in it.)