Carb and Throttle Problem

'79 kz400

I'm a technical idiot, trying to learn so please bare with me.

I think I may have several problems and not just one. First, the bike doesn't idle properly. Once you start it up, it wants to die unless you keep giving it gas with the throttle. If you can keep throttling it enough (several minutes since the bike hasn't been run in a while - maybe this problem will go away with more usage?), then eventually it settles down and idles at just below 1000RPM, but even then, if it sits for too long (maybe 10 seconds), it wants to die.

This problem may or may not be related to the second problem, which is that the throttle is wildly inconsistent. The slightest little touch will send it up over 4000RPM. Where is the adjustment for that?

Third and probably most important problem. I believe the bike is running "cold" or "lean" (is that the right terminology?). At higher RPMs, the bike burps as if the air flow isn't right. Something is wrong with the carburetor and I simply don't know what. Does it need to be jetted? What is "floating"? Are those terms synonymous? Any help would be greatly appreciated.

I can post pictures if anyone needs them in order for me to be more specific.

Hey King. I don´t know the first thing about the 400s, but these guys do:

www.kz400.com



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One of the shortcomings of the KZ400 carb is that the pivot arm the butterflies pivot arm isn't sealed well on the ends. On a BS Mikuni cv carb, the pivot arm ends are notched and have a small seal (looks almost like a valve stem oil seal in miniture) pressed in. Then they put a plastic washer over the seal and hold these in place with a C-clip. On the Keihin butterfly rods, the seal isn't nearly as good. Once they start leaking around the seal area, air gets into the venturi and leans the mixture and the idle will pop up, as described. Go find Odd Ivar on the kz400.com forum as suggested and ask him how he has fixed his carburetors in the past. Sounds like you may have some other issues but that is where I would start checking with your symptoms.