TOPIC:

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?

Check for leaks around the intake manifolds at the head.
Steve

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.

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.

Thanks guys these are great ideas. I'm still working on these issues, among others that cropped up.

Maybe slop in throttle cables, check adjustment