Iam running the same carb do you know what main you are runing also what is your elevation.I have parinoa about sticking pistons after owning a LT500 so Iwas increasing the main jet to try and make it stumble on wide open and I could never get it to. The plugs were alwas clean I was told that some times if you are too rich it will wash the plugs clean and not stumble .So I have been dropping main Jet sizes plugs now have color .