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The dreaded 6 k RPM stumble pick up wires good?

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  • #46
    Choke plunger seals baby!!! : D oh yeah!

    I swapped the XJ1100 carbs in and moved all the internals (over from my XS11 carbs (but forgot the idle air jets from the dynojet kit, darn it). IT'S GONE!!!
    THE STUMBLE IS GONE!!!
    THE STUMBLE IS GONE!!!
    THE STUMBLE IS GONE!!!
    did I mention it's gone?

    Only parts not swapped over are the choke plungers/seals and the butterfly valve seals. I don't think it was butterfly valve seals, cause they would have caused more problems at idle than WOT. The choke plunger seals, however, are up in the top bell of the carb and can feed right down the middle of the slide if they are bad. When the slides are all the way up, there is the largest pressure difference between the inside and outside of the diaphragm. In that situation, the leaky seals allow the enrichener to be in the "on state" even if the choke lever is closed.

    My only issue now is a little popping on decel even with 45 pilots and the mixture screws nearly all the way out. I put them at the same setting when I fired up the XJ1100 carbs, but it was a bit lean at idle (I synchronized them too, of course). Then I remembered that there is either a slight difference between idle air jets between XS & XJ, or maybe I changed them as part of the Dynojet kit install. But I remember they were different. So I need to pull them one more time to change those and then should be able to go back to 4 turns out on mixture screws, and the mild popping should be gone.

    The bike runs better now, and the choke/enrichener works better than it ever has before. I only use the enrichener for a few seconds. I'll figure out what to do about a lever next.

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    • #47
      Choke Enrichener seals caused wide open throttle cutting out

      One more comment to clarify: The bike now revs cleanly all the way to the red line with wide open throttle. No more stumble, no misses. Choke plunger seals (pretty sure) caused engine to cut out at WOT runs to the red line. The engine definitely feels stronger now, pulls VERY hard.

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      • #48
        Digging up an old thread, these symptoms sound very close to what my new to me '79F is doing. On my '78 when I had the "usual" coil pickup wire issues, the stumble was a bit more intermittent and the bike could "fight through" it. The current "cutting up" can't be "fought through," but from idle up to normal riding speeds and throttle openings the bike rides really sweet, like a nicely tuned stock XS1100 should.

        EDIT: my issue ended up being massively oversized main jets that a previous owner had installed for some reason!
        Last edited by gtem; 11-18-2024, 06:46 AM.
        Yamahas: 1979 XS1100F
        Past Yamahas: 1978 XS1100E, 1976 XS500C

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