KZ400 Idle issues. I'm stumped.

DoctoRot wrote: Hmmm, i will try the colortune tomorrow to see whats going on, i haven't used it since i really went through this thing. I bought the pilot needle washer and o ring brand new from kawasaki, and they are in there. is it possible the spark plug is not seating deep enough on that side? I read that that can cause carbon build up.

There is no reason why one of the plugs would seat deeper in the chamber than the other if both are the same.

DoctoRot wrote: The plugs look great when i just let it idle for 10 min with a fan in front of it. Only once its been ridden does #2 get sooty. i suspect the slight hesitation i feel in the mid range is a symptom of the rich condition in #2

Then, there are 2 different issues goin on. One of them the erratic idle, the 2nd, rich running of the main circuit of carb #2.

There's a large chance (happened to me before) that the float valve would not control fuel level accurately on one carb. Vibration from the engine interferes with the float valve and fuel level might go up until the float puts more pressure on the valve to close it, but at this point level has gone up making that carb run considerably richer.
I suggest swapping the float valves and floats between both carbs, reset float level (wet method) and see how the engine runs.

DoctoRot wrote: Is it possible the needle is not seating right in the holder? i guess i will switch them and see what happens. It still doesn't explain the erratic idle. Im tempted to buy a used advancer off ebay and new points/condenser so i can rule that out. There is something strange going on there. Could my cam chain be stretched out? I adjusted the tensioner and there doest seem to be any particularly tight/loose spot.

Regarding bits of the ignition system, as that of the 400 is a single coil wasted spark one, any issue would affect both cylinders. If cables, caps, and spark plugs are in good working order, points and condenser or advancer would affect both cylinders at the same time.

If you look closely to the pilot circuit outlets in the carb body, there is the main pilot outlet past the throttle butterfly on the engine side, and the pilot circuit bypass outlet right at the butterfly valve. If the butterfly is slightly open, the pilot mixture would flow out from both the bypass and main pilot outlets. Making sure the butterfly is fully closed, you must be able to adjust the pilot mixture flow with the pilot screw. This pilot screw does not have further action (or at least highly reduced impact) if the butterfly is slightly open as the pilot circuit mixture would flow through the bypass.
Again, make sure the butterfly(s) close well, and check out using the colortune plug the effect of the pilot screw. Keep in mind the pilot screw meters MIXTURE, that is, the AFR will not be changed, just the amount of mixture through the MAIN pilot outlet. If you have to alter the pilot circuit AFR, you will have to exchange the pilot fuel jet (as I believe the pilot air jet can't be)

undiablo wrote: Glad to know to joined the forum Z650Spirit! I am sure you will share all your knowledge with this great community.
Best regards from Buenos Aires.

Thanks! Regards!

Patton - I checked the wires with the ohm test. Im not sure what type of wires they are, they look like they are in OK condition. I think the coil is factory as are the wires, i dont see how you could replace the wires without replacing the coil The manual calls for B8ES and thats what i am using.

Pablo - I will try switching the float valves, Im pretty sure the butterflys are fully closed, i will check again when i have the carbs off.

Swapping the float needles did nothing. all the issues remain the same.

Pablo - I think you might be on to something here with the pilot circuit bypass. if i turn the #1 carb pilot needle all the way in the bike will nearly die, however if I close #2 the bike does not change idle at all. Interesting, I'm going to inspect that carb again.

Cool, let us know your findings, Vic.

I'd say reset the pilot screw to the same value as in carb #1, and re vacuum sync both carbs, first off. Your aim here is to have both carbs running on the same adjustment value as possible.

the butterflys seemed to not quite be closing all the way so i readjusted and reinstalled. IDLE ISSUE GONE!!! however it still was hesitating at the middle of the power-band, and rich in #2.

I then switched the slides and needles in the carbs and it drastically reduced the hesitation. It will rev all the way to redline now under load. A very slight hesitation remains, and it still was a bit rich in #2 though. I have bought some OEM needles off ebay. The spark plug wire for #2 seems a bit fiddlly at the coil connection so Im going to order a new coil and wires just for peace of mind.


Getting close to solving this thing, any suggestions?

Good to know she's running better, Vic.

As regarding the main fuel system, I suggest you remove and check out closely the bleed pipe on both carbs (amount of holes in them), and primary and seconday main air jets and passages to the bleed pipe and needle jet. Search for the tiniest differences between them.

To be absolutely sure of the passages flow I usually pressurize them with a pvc hose from a water tap to see how water flows out the other end of the passage. Then blow with compressed air and heat the carb up with a heat gun to dry them out completely. If the carb proves clean, this whole process would take no more than 10min/carb.

Thought I would update this. I cleaned the carbs thoroughly again, installed new coil, and OEM needles. Still a tiny bit rich on #2 but throttle response is crisp and no hesitation occurs, its fine for now. My friend I sold it to has been riding it everyday to work and he already wants something bigger. I think I might sell him my 650 and get a bike more suited for my 100 mile round trip commute. I'm thinking superhawk...

I drove my KZ400 to the top of Mt Evans Colorado at over 14,000 feet... With my 9 year old son on the back!! About a 75 mile round trip afternoon.

Wow that is impressive for that little bike. PIcs?