just got top end together started right up.put a 250 main jet in rode for about five minutes to start break in gets to a certain rpm then makes like a crackling noise.rode little longer died on me.got it to start.checked plug wet and black.so i went to change my jet to a 240 and the thing the jet screws into goes up and down before it wouldnt is it supposed to?is there supposed to be a little washer that goes on there with that plastic piece?