A friend of mine has a 80cc(66cc) flying horse with around 300 nmiles on her. As soon as it starts it makes a horrible knocking sound, the wierd thing is it goes away about 3 minutes after it starts? The motor accelerates normally. I thought maybe it just needed extra time for lubricating, but if you run it till it goes away, then shut her down and re-start her again right away, you have to wait another 3 minutes for the sound to go away. Confused, I told him I would like him to buy another motor, and rip this one apart to see what is up. Anyone hear anything like this before?