Have a 1990 yamaha15 horse. Had probs with maintaining smooth idle , although at high rpms runs ok. Stalls unless giving throttle. Brought to mechanic(friend recommendation), who first rebuilt carb. Was ok for 1 month then same again, this time claims one of the float supports was broken and now needed new carb. So now we get a new carb, but still the same....although compression on cyls was fine from the beginning. Now takes top cover off and claims that the piston has a small bite out of it...from water he says...I could barely see it...compression still good...I said I couldn't spend more on the motor than what it's worth in running condition(700), so we agreed to cut our losses, he let me have the new carb, and put a new gasket and closed her up.....Is it time for a second opinion?, before giving up. Does it matter that the mechanic seems to deal with johnson/evinrude and very little with yamaha? My son (his motor) is devistated. Any Suggestions/comments. Thanks