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Fouled Spark Plugs


New member
Just got my RT back from the dealer after it's 600 mile service. They had to replace all four plugs due to the carbon build-up. I saw the plugs - they looked pretty bad. The dealer thought the amount of build-up was very abnormal, and said that it's due to me lugging the engine. Problem is, I don't think I've really been lugging it. I've usually been shifting at 4000, the max allowed during break-in, or sometimes a little higher. For steady riding, I normally kept it between 3500-4000.

Is the dealer right, and I just need to ride at higher RPM? Or could there be something wrong with the bike?

Thanks in advance for your comments.

P.S. I agree with all those who've posted about how much better the bikes run after that first service. Less vibration, smoother shifting, and the bike does seem happier at higher revs.
fouled plugs

Dear Texas RT: I live in Sherman, northeast of you and am a former dealership airhead wrench, riding a newer R1150R. Carbon plug fouling on any engine indicates a weak spark, fuel delivery/air flow problem or the wrong heat range plug. Are they Champion plugs? With the bike cold, rub your fingers in the end of the muffler and see if you get a lot of dry black soot. You should get no more than a very light black smudge. If the problem continues, you'll soon have serious carbon buildup in the combustion chamber and pinking that won't go away. What you see on the plug is also accumulating on the piston crown, combustion chamber and valves. Hope this helps.
I generally don't ride our oilheads below 4000 rpms unless I'm piddling around town. Even then, I'm more likely at 3-3500 rpms.