This subject has been pretty well driven home on this thread but I can't resist saying it again. I was at the field today and an older member with probably 40 years of experience was tuning the high needle on his fairly new 150. He had likely gone more to the lean side than you should but I would hesitate to say he had even peaked the r.p.m. He had removed the jam nuts and was only using the washer and a threaded spinner nut. It backfired with no warning so violently that it tossed the propeller at least 60 feet forward and to the right of the plane. It missed his head by probably 4 inches. He was saved by blind luck. I would bet if it had hit him even in the torso and flat he would have been on his way to the E.R. I will NEVER stand by a running prop. without FULLY EXPECTING that it is coming off. I have been an automotive and heavy equip. mechanic for 22 years and I've seen some spectacular mechanic failures, but I learned a lot of respect for these little glow motors today. Take care, Cliff