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Author Message   Perry Posted on Friday, May 29, 2015 - 05:53 pm:        I did some work on my '05 XB12scg (full Buell race kit) over the winter (replaced oil pump drive gear, which means removing heads, etc.) and now it runs well at any RPM except when the throttle is wide open (or nearly so), in which case it starts to sputter about 4000 RPM so much it can't get above about 4500RPM unless I back off the throttle, and then it revs smoothly through the range. Somehow at heavy throttle things aren't happy at all above 4000RPM. Has new plugs, and just replaced the air intake and exhaust seals, did TPS reset, and it runs well at low to mid throttle. I rode around a bunch to be sure the AFV is right and it made no difference. Could it be fuel filter after sitting all winter? Something else? How do I debug and diagnose this?   Bugkodee Posted on Sunday, June 07, 2015 - 02:51 pm:        Data logging?   Perry Posted on Sunday, June 07, 2015 - 03:04 pm:        Well I figured it out myself - here's the story for the benefit of anyone else who may have the same issue: Given that it sputtered only at heavy throttle I figured it must be getting starved for either gas or air. Forcing the sputter in the garage produced an exhaust that smelled like a "rich" mixture. So, I removed the air filter and airbox and tried again - and the problem went away. Hence, clearly it was starved for air. Removing just the air filter did NOT fix the problem, so I knew that wasn't it. Careful examination of the velocity stack led me to notice that the rubber stack wasn't fully seated down far enough onto the throttle body. This caused the velocity stack to be too high, much too close to the inside top of the air box with little clearance for the air to flow - so when there was heavy air demand, it just couldn't suck enough air through that tiny gap. After battling the velocity stack and clamp for another 20 minutes, I was able to get it seated properly - Problem Fixed!   Bugkodee Posted on Sunday, June 07, 2015 - 03:44 pm:        Good tip! Does your stack not bolt directly to the throttle body?   Greg_e Posted on Sunday, June 07, 2015 - 11:46 pm:        Interesting find.   Firemanjim Posted on Friday, June 12, 2015 - 12:02 am:        See this alot-- if you run finger down stack it is smooth transition if it is seated fully, if not you can really feel it! Only the early XB's were attached with allens.

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