A friend of mine recently upgraded his Tailwind from a stock O-290 to a souped up O-320. He had used a single electronic ignition with automotive plugs and mag with aviation plugs for years with the 290 engine with no problems. The new engine would run fine at full power with the same set up for about 80 seconds then sputter and backfire until he pulled the throttle to idle. We spent weeks looking for the problem with the fuel system but after each mod we could still only get 80 seconds of full power. Finally I noticed the tips on the automotive plugs had color pattern that indicated they had been very hot. We change to aviation plugs and have had no problems since with the ignition system. We suspect we were getting pre-ignition. Only 80 seconds of power made for an exciting first flight after the engine change.

Rusty