first..check your timming..see if it's in time ?..as for the muffler..you may have a hard time fiding that..the parts for these bikes are getting harder and harder to find..as most are no longer being made...for your carb over flowing..either clean the carb really good !..or over haul it with a new carb rebuild kit.anyone know where i can get a decent factory muffler for my 87 trx350 4x4? or want to trade factory for the cobra i have? ebay has one but its got holes in it and they want 90 bucks. having trouble tuning my bike and i want it quieter for hunting. cleaned carb many times, changed jets still dies when wot is applied from idle. whats got me baffled is i had some dirt in the float needle so it was overflowing. when leaking fuel the problem went away? reved up fine but cleaned it and the problem came back. cant adjust float level but would that be it? i also sometimes get a backfire and a flame out of the carb when the boot is off.