I was having a stutter or popping while accelerating. Didn't happen all the time. I have 8,000 miles on the rebuild. Went to dealer pickup new Spark plugs. Bought the stock gold HD plugs. When I puller th front plug it was perfect color. Light tan, no excessive wear. Gap was good. Pulled rear plug.. It was a darker grey. Gap was good. Little carbon color to it. Neither had any moisture on them. Ran bike this morning no more popping. Question is would plug be bad after that many miles? If it wasn't firing correctly. Wouldn't it be fouled? Would it be better to have a hotter plug. Where the jug with the carbon was?