I have an odd problem with a 50 cc air-cooled two-stroke scooter engine that keeps locking up at full throttle, then freeing up again.
I just bought the bike second hand with a new belt needed fitting. I have pre-mix oil/fuel in case the oil pump keeps failing.
It ticks over no problem and has plenty of pull, but when I apply full throttle for more than a minute the pitch of the engine drops suddenly, and the engine seizes and the back wheel locks up. I don't know why it is seizing up.
I had the head off and checked the piston and barrel and rings. All look good. I really have no clue now why this is happening.