Guy,When you turn off your ignition switch, it immediately stops generating sparks in your spark plugs. The engine still makes a few revolutions and still has fuel/air mixture being drawn into the engine through the intake valves. However, because you don't have a spark in the spark plug, the fuel/air mixture doesn't ignite and the engine just cruises to a halt. With engine run-on (sometimes called dieseling), something inside the combustion chamber is so hot that it continues to ignite the fuel/air mixture in spite of the fact that the spark plugs are not sparking. Some of the things that I've heard of that can cause the problem include: 1. built up carbon inside the combustion chamber as a result of having run the engine with bad spark plugs in the past 2. spark plugs that have accumulated carbon on them but have not yet fouled out 3. cheap, low octane gas that ignites at much lower temperatures that higher octane gas requires 4. timing advanced too far So, having said all of that, I think I'd first install some new plugs, then run some top-end cleaner additive through a couple of tanks full of gas, try buying some mid-grade gasoline for a couple of tanks of gas, and check the timing. Good luck. I'm sure that you'll get many more opinions of how to fix this problem. Tom
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