Carbon Build up On Pistons 1 and 3.

[Boozy Creek Beast]

I just pulled my top end apart and noticed that I have an excessive amount of Carbon build up on Pistons 1 and 3. Not just your normal build up but enough build up that it almost filled my Valve cups. Piston 1 is worst than 3 but both are bad. 2 and 4 have what I would consider normal carbon build up. I did a 1100 mile weekend trip last year as my final ride and then put her down for the winter. During the trip my riding buddy kept mentioning how rich my bike was running. He kept telling me that he couldn't ride behind me any longer because the gas fumes were makeing him sick. I new it was running rich but I did not think it was that bad. I guess my question is would running the bike with a very rich air fuel mixture cause such a large carbon build up? If not what would cause this problem.

The Beast

[RacingJake]

Yeap excess fuel can cause a build up problem. You should see a motor after using racing fuel, it burns much cleaner and the pistons still look like new.

It happens alot on Harley's too with the fuel enrichment knob, choke

Check the choke to see if it's all the way off. Fuel level set to high in those carbs or needle valve leaking, also jetting may be causing it.