What I would do is if it ain't a tank problem then I would check my Temps but the easiest way is just see if your pipe is getting cherry then you know the timing's off but if it just seems like the carbon is building up what I would do if I was you was run Marvel Mystery Oil instead of 2 stroke once a month but to feel better about it I usually mix it half-and-half with two stroke oil when you pull the head the next time it will look pristine but that carbon is actually a good thing it lowers the temperatures on the piston try a hotter plug NGK five or six if you're on an eight or 9 now I have tens that are super cold but they're non-fouler racing plugs I only use them when I'm running really really hot timing and by the way we should ride sometime I'm in Bethlehem right now I'm out of a bike and I'm waiting for a replacement.