1977 KZ 650 Off idle engine stumble when hot?

Hello all,

Been riding this new to me antique a lot, about 750 miles the past two weeks. All routine maintenance completed. Bike starts, idles and runs great, but seems to have a stumble off idle after up to operating temp. I am going to move through the FSM idling procedure again. When warm it idles fine, at first movement of throttle to engage first gear, it stumbles and will die without jiggering. No problem on shifts and other gears. I am think air screws are too lean, but what say ye?

Okay. Got the carbs fine synched with vacuum ghages. Idle is fantastic. Purrs like a kitten. It has a slight of idle stumble still. It is much better and won't die but it's there. All maintenance done not sure if this is it or if I have missed something. Good power in all gears. Any ideas?

rrsmsw9999 wrote: Okay. Got the carbs fine synched with vacuum ghages. Idle is fantastic. Purrs like a kitten. It has a slight of idle stumble still. It is much better and won't die but it's there. All maintenance done not sure if this is it or if I have missed something. Good power in all gears. Any ideas?

Amazing how much better the engine idles when one or more carbs is not fighting the other ones!!
Stumbles off idle are most likely a temporary lean out. If all else is good, using pod air filters is usually the culprit.
If you do not have an accelerator pump carb setup, it will require a slightly richer idle mixture setting and possibly a richer pilot jet.
I just found that rolling the throttle on quickly, rather then snapping it WFO, pretty much removes the stumble.