An engine only needs fuel, air, compression, and an ignition source to run.
After you shut down your ignition, the heat causes the engine to run like a
diesel, using only the compression and the heat to fire.

It's bad for the engine. In the old carb engines, there was a dashpot that
shuts off fuel when you shut it down. I don't know what the equivalent is
for fuel injected engines.

First thing, though, is to do a complete tune-up, including air filter.
check the timing.if it's too advanced, this will cause the problem. Your
plugs could be too hot for your conditions. Try and run the next cooler
number. make sure your cooling system is in good shape. Also the
exhaust..........HTH.

MM^^