Re: How do I know if?
A #2 piston issue is not that uncommon on those motors. There were quite a few service bulletins out on them, make sure you're up to date on them all. OMC actually danced around the real issue but there was a reason which isn't important now.
Those motors run pretty lean in the mid range & cruise rpm. You're running on full advance timing but not a lot of fuel. The middle cylinder naturally runs the hottest. On a long cruise in the mid range the middle piston can indeed become damaged. Your mechanic was probably grasping for straws when he mentioned a stuck needle valve. However, he was on the right track. If you saw the damaged piston it most likely had a lot of skirt damage which leads you to look at fuel supply.
Because the motor is running so lean in the mid range we found that going richer on the mid range jet stopped the issue 99% of the time, given everything else was in proper working order.
Oddly enough if someone ran that motor wide open all the time it would almost never fail. Still full advance timing but you're dumping a lot more fuel once you get into the hi speed jet.
Start with the basics. Make sure the timing is correct. Make sure you have the right Champion plugs, I'd opt for the slightly cooler options. Make sure you run fresh 87 octane and a good TCW III oil. Make sure the top rpm is between 5800-6000. Once you verify all that if it were mine I'd go a couple numbers richer on the mid range jet.
