Idle RPM has a mind of its own ...

  • SpeedBump101
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05 Jun 2020 09:40 #827360 by SpeedBump101
Idle RPM has a mind of its own ... was created by SpeedBump101
I finally got my 1982 KZ 750N Spectre running, but it's having some trouble just idling. We had it running for a while, the engine warmed up nicely, but once hot it decided to randomly rev itself into the 4000 RPM range without any impetus from the throttle. Such spikes did not drop until we fiddled with the choke a bit, and this happened several times. At the end of the night, after adjusting the idle screw and backing the fuel mix jets out from 2 to 2.25 rotations out, it still spiked RPMs.

I recently (this past month) cleaned and rebuilt my Keihin carbs, noting that the floats were freely moving.

Is there something I should reset or adjust in the carbs to control its idle speed, or is this a problem in the engine or airbox?

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  • SWest
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  • 10 22 2014
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05 Jun 2020 10:20 #827365 by SWest
Replied by SWest on topic Idle RPM has a mind of its own ...
Check for leaks around the intake manifolds at the head.
Steve

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23 Jun 2020 10:09 #828739 by gavroyer
Replied by gavroyer on topic Idle RPM has a mind of its own ...
Might be a good idea to double-check that your spark advancer isn't getting stuck in the advanced position as well. Super advanced spark can make the engine rev weirdly too.

1980 KZ440-A1 LTD

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23 Jun 2020 16:15 #828778 by Nessism
Replied by Nessism on topic Idle RPM has a mind of its own ...
Instead of checking for vacuum leaks I'd just replace the rubber carb boots that bolt to the head. If yours are not hard, brittle, and leaking, they will be soon. And it never hurts to lube the advancer too. Great suggestions.

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03 Jul 2020 10:14 #829690 by SpeedBump101
Replied by SpeedBump101 on topic Idle RPM has a mind of its own ...
Thanks guys these are great ideas. I'm still working on these issues, among others that cropped up.

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26 Sep 2020 07:58 #835682 by 79shaft
Replied by 79shaft on topic Idle RPM has a mind of its own ...
Maybe slop in throttle cables, check adjustment

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