OK, Ive had a 4 stroke for one day. Yesterday, it started and ran great. I ran two tanks through it for break-in, and started it 3-4 times after. Today, it "popped back" and spun the prop nut off two times. The third time, the spinner backing plate exploded when I tried to start it.. OK........ What the heck is going on?? The high speed was 3 out, per brake-in instructions. Any idea's?

Scoot