Mechanic just replaced the carberator, not sure if it was running properly before. So he replaced it threw the muffs on it fired up and ran like a top. Said it got great compression. Took it to the water fired up, threw the gas to it and it died. Finally got it to run by giving it full power and it sputtered to a go. She runs about as fast as Phelps swims at full throttle. Is this motor toast? any ideas on it if not is appreciated...thanks