Took the carb apart today and the washer (it is not an O-ring) is on the main jet, so that is not the problem. One last thing, when I ordered the jet kit I asked if it was necessary to have the muffler modified also. I was told it was not, so I am still using the unmodified stock muffler. Is this correct? Do the new Kientech jets need a muffler that flows more freely than the stock muffler? Thanks.