It's hard to tell, but it sounds like a mixup to me. It is probably the needle or e-clip that is too lean, or a carb air leak. The main can be whatever, but you are on the needle 75% of the time. Rarely does the main cause this unless you have it hammered continuously. This is not a seizure since there is a hole. It's a burndown. Did you personally see the piston? Wiseco's usually sieze first.

 

[img]i/expressions/face-icon-small-shocked.gif[/img] I just have to respond to this. First the dealer has no idea what he is talking about. rich condition does not burn a hole in a piston. You a getting bent over on this one. There is only two things to cause a hole in the top of a piston. Lean condition or inproper timing. Sounds like the carb was not all the way in engine flange or if they had the crankshaft out they didn't install the stator back in the same spot (timing). Maybe crank seal Or maybe they did mix up the carb with someone eles which is hard to believe. Usually you leave the carb on the machine when doing a top end. There is one thing for sure if you have a hole in the piston then the crankshaft will have to come out this time to clean the metal out. If the machine was only run at half throttle when this happend make sure the jet needle e-clip is in the proper spot. The guy also has to tell you exactly what happend. Was he at full throttle or not? When you put this thing back together. Make sure crankshaft is removed and cleaned and checked for and bad bearings. New crank seals and all new gaskets, make sure piston has proper clearence according to wiseco papers that come with piston. Engines with wiseco pistons need to be properly warmed up. They will seize if not. Make sure all carb jets are the correct size according to the book. Go up one size on the main jet with a overbore until you have a chance to check the plug. also check jet needle. If you really want to bullet proof the piston then send the new piston to Swain Tech for a coating. They will ceramic (spelling?)coat the top and molly coat the skirts. No more burn downs because of the ceramic top. And no more scuffs because of the the molly coating on the skirts. All this for aroung $32.00 a piston. I hope this helps

 

I am guessing the problem has gone away by now. The post was done on this November of 2000, 15 months ago.