Motorcycle Repair: stuck at 6000 RPM sometimes when hot, online spell checker, kawasaki kz 750

Question
Bill,

  I have read the AllExperts' how to for cleaning and adjusting the carbs on older bikes. I found it useful and have applied this know how many times on Hondas, Suzukis and Kawasakis. I am sure the problem I am having is not a carb problem because using 2 different sets of freshly cleaned carbs the bike behaves the same way: when it gets hot and you wick the throttle in neutral it gets stuck at 6000 RPM. The only solution is to hit the cut-off, or if she is rolling, engage the trans. I have also cleaned and reassembled the mechanical advance (it moves freely like new). This bike is an '83 kawasaki KZ 750 Spectre 4 cylinder, which I recently completed a top-end on. I live in Monterey where the MotoGP is held in July. Lots of cycle enthusiasts here will have a sour opinion of my rebuild abilities if I cant work this out. Do you have any idea what could be causing this? Thanks and, this new online spell checker is great.

R/ Bill Lynn
wrlynn@comcast.net

Answer
Bill, you are getting me out of my Honda comfort zone again! :>)
Either your carb overhauls are very consistent with some small mistakes or something else is happening!

For the most part, the main things that cause high idle revs are air leaks, low fuel levels, spark advancer problems.

Sounds like you have covered most of them, so far, but you didn't mention if the throttle cable was old/new and or if it was routed properly.

The other things could be any kind of air leak at the manifold connectors that appears when the motor is hot.
Somewhat more esoteric would be the vacuum operated petcock diaphragm having a pin hole and/or a blocked fuel screen that reduces fuel flow, so that the float level is temporarily lowered after a hard run, causing a lean out condition.

Make sure you have a little cable slack in the throttle when it is at idle and the routing is okay. If strands are coming loose inside the throttle cable, they can act somewhat intermittent, plus turning the handlebars back and forth can reveal a misrouted or misadjusted cable.
It doesn't sound like your carb overhauls are causing it... check the bike for the source of the problem.

Bill Silver

I second your thoughts on the spell checker, too!