There are drain holes in the bottom of the silencer so you won’t be able to kill the motor by plugging up the ends. If the carb and compression are ok, how’s the spark? If the motor has it’s original coils in it, I can guarantee they will be cracked and will need replacing. Cracked coils can let the motor run for a while but as they warm up they will start to fail. If you remove the inspection cover on top of the flywheel, you will be able to see what your coils look like. If they look anything like the ones in the picture, it’s time for repairs.
