80 KZ750 carb question

Hi guys,
New to the forum. WOW, lots of good info here. I have an '80 KZ750e engine with CV carbs in a mini-sandrail and recently sent the carbs over to the local Kawasaki dealer to have them cleaned. The donor bike ran awesome two years ago but sat for that long also and now with it mounted in the rail with the stock airbox and new aircleaner it was not idling or transitioning smooth. Now that I have them back, it idles awesome, transitions great, but it will not come back to idle, it is screaming. I let the clutch out to put a load on it and then push the clutch in and it is idling fine again. Any ideas? Vacuum leak? I checked throttle cable and it is returning. Could leaking boots on the carb cause it to do this or would that just cause bad idle?
Thanks
Kurt

Post edited by: model avionics, at: 2006/01/12 13:09

The 750 used both Keihin CV34 and Mikuni BS34 carbs depending on model and year. Which are yours? Could be an air leak in the pilot system or could be other issues but this sort of depends on which type carburetors.

They are Keihin CV34.

it wouldn't be an air leak, because it would just rev right up again, Does it come down eventually without putting load on it? My dirtbike does that (not as bad) and I was told that means your needle and seat are worn out and need to be replaced.

The CVK34s are not all that prone to doing what you describe. Most likely candidate for causing the problem is the throttle cable. Not only must it shut but it must have some slack in it. If you have a motorcycle style cable, look at your right hand switchgear and there is a barrel adjuster on the cable with a locknut. Loosen the locknut. Watch the cable end near the carburetor assembly and turn the barrel toward you some to gain some slack in the cable.

The next possible issue is that the carburetors are binding somewhat and not allowing the choke butterflies to fully seat each time. To fix this, you can usually remove the assembly from where they are mounted, loosen the screws or bolts that retain the four carbs to the rack that holds them and retighten. Open/close the choke butterflies to ensure that none bind and cause one or more of the butterflies to remain open.

Last issue is that when it was rebuilt, perhaps whoever did it did NOT change out the very small and thin rubber o-ring or perhaps left them out when replacing the mixture screws. There is a rubber o-ring with a small steel washer under the mixture screws to seal them. These are CRITICAL to getting the bike to idle because if they are not installed or installed improperly, the bike will race like all get out at times at idle.

I listed the problem solving steps in perhaps the most likely order they would solve the problem. I am pretty certain one of the steps will solve your problem. You also have instructions somewhere in a shop manual to lubricate the pivot points for those choke butterflies I think and that should also be done...

Wiredgeorge,
I did check the throttle cable and linkage and all is good there. I noticed around the 1,2 and 4 intake boots while it is running that there is a wet area around where the boot mates to the intake. I sprayed carb cleaner there and it slowed the idle to almost dying.I will disassemble the carbs and check for the o-rings you mentioned on the mixture screws. I took the intake boots off and they are cracked pretty bad so I red labeled 4 new ones. I'll go buy a manual so I have a better clue of whats up. I was hoping the local Kaw guy's would make it so I would not need to touch the carb's. Might be a phone call in todays schedule. Thanks for your help,,I'll let you know what I find
Kurt

I have no idea what "red labeled" means but you had best get new intake manifolds ASAP. Cracked manifolds concentrate cold air on the piston crowns and WILL zap a hole in the piston in short order. You CAN NOT tune carbs with cracks in the intake manifolds so I recommend you wait and see how they run BEFORE you start dissecting them. Tune them AFTER replacing the manifolds. You can't sync or set the idle effectively. Cheers!

Update,
I took carbs back to Kawasaki and they went through them again just in case. I installed the new boots and same thing is happening. I checked compression and it is a little low(60-75 psi). I sprayed carb cleaner everywhere while running and there is no effect on throttle now. I checked timing advance to see if it was stuck but it is OK. Any more tips?
Since this was removed from the bike the vacuum lines that use to go to the vacuum switch for the PCV setup have been removed and they put plugs on all four of the carbs(no leaks when sprayed with cleaner). The black PVC canister is not on either. The two vent tubes on the head are hooked to each other with a short piece of tubing and the port on the top of the air box has a plug on it. The port on the bottom of the airbox is still connected to the crankcase. It does seem now that maybe it is not the carbs doing this but I am lost for an answer.
Thanks in advance,
Kurt

I think I found it.
We took apart the timing advance mechanism and cleaned it real good and it was a little better, it seemed to want to come back to idle. We put a zip tie around it to keep it from advancing and blipped the throttle and it went right back to a nice idle. I guess the springs are bad? Can this happen from sitting for two years? I'll try to get some new springs and see what happens. Only thing open tommorrow is the automotive shops, any ideas on a useable substitute to test this, something like the springs in an old style mechanical advance distributer for Chevrolet? This is getting exciting!! It might run smooth soon.