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Thread: 453 starts running real rough at 8K RPM: why?

  1. #71
    KTMTalk Member
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Quote Originally Posted by caflash View Post
    your flywheel, pickup and coil and wire and cap for your testing are here for the pickup
    Bob, I tried your coil, wire and cap. And a new plug too, with a terminal nut to fit your cap (plugs I had on hand only had studs). Same symptoms persist. Flywheel and pickup swap to come.

    Quote Originally Posted by Eli View Post
    I would swap to a known good carb, personally.
    I have a FCR-MX on the way to try. I don't know what specifically could be wrong with the current FCR slant carb, I've been through it and according to me it's good, so I agree about just swapping in a whole carb to check.
    I don't wanna pickle.

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  3. #72
    KTMTalk Member
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    Default Re: 453 starts running real rough at 8K RPM: why?

    Update on all this.

    I got a carb from a parted-out 2004 450 EXC. A 2nd generation 39mm FCR MX in not bad shape. I went through it and replaced a couple things, cleaned and blow-dried, installed and... wow. Already much better. Fiddled with jetting to try to make it even better, now have it with 45 pilot, 165 main, JD red needle at #4, and the bike revs smooth to 10K. Feels like it's supposed to. Very nice.

    So those who had the fuel issue bet, collect your winnings. (Not me, I thought it was more likely ignition.)

    It's still a mystery to me what is up with the original 1st gen 39mm FCR. I had gone through it and dealt with everything that looked at all questionable. I tried a bunch of jetting combinations with no real improvement. Travis suggested that the HT Racing intake bell and vane could be the problem. It sure isn't physically matched to the airbox in any clever way. Maybe it is restricting airflow enough to make the whole usual range of jetting combos too rich at high RPM? I could swap the stock intake funnel from this FCR-MX carb and test that. But right now I'm tired of troubleshooting this bike, I have something that works, Ima go ride.

    --Paul Q-B
    I don't wanna pickle.

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