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Thread: Carbon build up....

  1. #1
    Senior Member Chicknstripn's Avatar
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    I've torn my engine apart twice. Once at 37k and then 5k mile later due to a transmission issue. At 37k I noticed both pistons had quite a lot of carbon build up, however, I figured this was just normal for a bike with 37k. The second tear down, after only 5k on a brand new motor, the amount of carbon build up got me wondering if something is wrong with my set up. In both cases the front cylinder had less then the rear.
    The amount of build up after 5k was enough to almost completely cover the top of both pistons and about the thickness of a heavy construction paper.
    I run only 93 octane fuel and I'll occasionally add some fuel injection cleaner or an ounce of seafoam.
    Any ideas as to why I'm seeing so much carbon build up?

  2. #2
    Senior Member mrlogix's Avatar
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    what was the appearance of the carbon? satiny and hard or kind of soft and flat black like candle carbon. Carbon coating can happen very quickly (to a point) even in the best tuned engines and is normal. The additives that the petroleum companies put in the mixtures when blending summer and winter fuels can cause carbon build up (normal type-minimal thickness kind of hard and dry and a little satin shine). What did the plugs look like? You mention tearing the engine apart twice, did you rebuild the first time? New rings, Valve job?

  3. #3
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    What kind of tuning have you done? Heavy carbon is usually the result of a rich tune. Its not uncommon for these engines to build up pretty heavy carbon though...

  4. #4
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    Any advice for getting and keeping the carbon out of the engine would be awesome as it appears to be common with the XB engines? Wonder if ethanol gas makes it worse? When I first got my 09 Uly it had 13K miles and the dealership somehow cleaned the carbon out of the engine. It pinged like crazy, really crazy, during the test ride and it made a huge difference to have it cleaned out.

  5. #5
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    Install a wideband and tune leaner.

    You'll never get rid of all of it, but the closer to stoichometrically ideal the less carbon build up there will be.

  6. #6
    Senior Member Chicknstripn's Avatar
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    First rebuild EVERYTHING on the top and bottom end was brand new. Only thing I reused was the transmission(big mistake) and the clutch.
    The carbon build up does seem to be the "normal" type. Took a little bit of work with and old toothbrush and brake cleaner to remove it.
    Plugs look slightly "hot". A slight burned looking ash if you will. Normal as far as I can tell. After first rebuild I switched to NGK dcpr9eix iridium plugs. Had the non iridiums first 37k.
    I have a Buell race ECM. Bike is a 200712r. It is now a 1250 with cams and stag two head work. I've never tuned the ECM.
    I'm sure tuning would greatly reduce the carbon build up.
    I'll wrench on anything any day of the week but when it comes to messing with the electronics/ECM I get a little gun shy.
    Thanks for the responses guys

  7. #7
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    What cams? Definitely needs tuning with the combination of work you've done. I would suggest putting your timing back to stock, it'll probably like it better with cams, head work, and higher compression. Unless you feel confident enough to get some dyno time in to really tune the ignition. Other than that, hook up a wideband to it and do some data logging. With a wide band do some controlled throttle runs and monitor your AFRs and make a not where you are at on rpms and throttle position. Might be helpful to Mark your throttle at 1/4, 1/2, 3/4, and WOT so you can see if you are too rich or too lean in any specific cells on your fueling. Datalog and then adjust accordingly. With a hopped up motor a WB O2 sensor is a wise investment.

  8. #8
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    Race kit/tuned bikes run rich. More carbon
    have a very high mileage stock set of pistons which are just bronzed over from borderline good tune/lean I kept since the rings were almost seized to the piston & crank went bad.

    Any race ECM/tuned motor I pull apart has more carbon than a stock ECM stock kit bike.

  9. #9
    Senior Member Chicknstripn's Avatar
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    Would a wide band be a plug and play upgrade? Or does it require any additional "stuff"?
    Timing was set at stock.
    Will be once it's all back together.
    Would love to get on a dyno and have the tuning done right. That might happen this spring.

  10. #10
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    If you got a kit such as the innovative mtx-l or spartan wideband youd have to wire it in, weld in the exhaust bung, and find a place to mount the gauge. So it'd take a bit of mechanical skill.



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