I hear ya. Used to on my dirt bike, if I put a good bit of load on it, say going through deep sand or deep mud in too high of a gear it would ping and make noise, but then I richened up the main jet and I gained power and the pinging went away. Just thought maybe it would be of help since nobody in here really mentioned that (Not to say that I assumed you didn't know it, of course.) If you don't have one around, I have a plastic nozzle here that you could give a shot for reference. I measured the bore on it last night and it was at 84 and some change.
