I have a 92 yamaha 480 that is bored .20 over ( I got it that way) that has a habit of burning a piston.To hopefully get it to run richer I made the change to the carb, replacing the primary nozzel with the 3 and putting the additional hole in the secondary. It starts and idles fine but bogs and will not rev up. cleaned the carbs and jets many times, went back to the standard main nozzels nothing seems to make any difference. I have good spark but is it possible that one cyclinder is dropping out when throttle is applied? Any ideas of where to go from here?