i have a 2003 kdx 220r that i just bought. i has had very few tanks of gas about 10 less . it was running great and then all of a sudden this low noise of under water running , or muffled sound this had happened shortly after flipping it over back wards . and running for a mile or so of trail i thought i might have got something up the pipe. i removed the pipe and every thing is clean . i rode the bike today after putting in a new plug and it still takes alot for the power band to kick in . and it does not have that crackle when you twist the throttle . but it will run good at top end or when you really get on it what gives ! i have a fmf pipe but im not sure of the model it was on when i got it . i also run castor 927 oil . there seemed to be a good amout of carbon in the main pipe for a newer bike . it has been awhile since ive owned a 2 stroke