The engine, 2gm20f, had not been started in several weeks. After failing to start after several tries, I was about ready to crack the injector fuel inlets to see if that helped. Before doing that I tried starting one more time. Thinking back, my finger may have slipped off the starter button and I quickly re engaged the starter. Then all hell broke loose. The starter had a difficult time turning the engine over and the low oil pressure horn and light came on. After maybe 1-2 seconds I released the button and dove down to check the engine. Heavy smoke was billowing out. I'm thinking electrical short or a fried starter motor. But I'm almost certain the smoke was exhaust fumes. After some research I am convinced the engine did a little kick back and started a backward rotation forcing the exhaust fumes out the air intake. Later, I bled the injectors and the engine started and ran fine. Anyone ever hear of a Yanmar trying to run backwards?