Sudden high idle while riding or parked

WG, or anyone... I have my 79KZ1000 ST up and running but I have a strange problem.

Sometimes the engine rpm goes up to about 4000 to 5000 rpm with the throttle closed. Since the carb slider is held in the idle setting by the cable it can't be because the slides are sticking in the up mode. There's no slop in the carb cables.

Once in a while it also spits back out of one or more carbs. It seems to be running very rich at idle.

It otherwise runs strong and does not bog or sputter when you give it the gas.

I've seen others on here with similar problems as mine but I've yet to read any cures for the problem. Any ideas????

It has new coils, plug wires and caps. The advance mechanism operates freely and was cleaned and lubed. The timing can't be changed, its electronic as you know.

Thanks in advance...
Bob

Give your intake boots a look-see. They might be cracked. Any slight crack would only get worse when warmed up. I've experience this before myself.

I had the boots that the carbs mount to off and they looked a little checked and old, but I couldn't find any cracks.

If I don't come up with any other options I will remove the carbs again, and again, and again...I can do it with my eyes closed by now.

Thanks for the reply,
Bob

while it is idiling spray a little carb cleaner around the intake boots, be carefull though dont just blast it full pressure, typically if you have a leak this should make it apparent, do you have a manual, make sure all the fuel and or air screws are turned the same on all the carbs and verify the sync.. typically it is a lean condition that will cause a fast idle

Katjbus: I'll try that too. I can make it slow down to about 1100 rpms by lugging the engine down. But it does it again when I'm shifting from gear to gear. In other words, the rpm's don't come down between shifts.

Thanks for the reply,
Bob

The choke plungers are shot. When you are sitting there idling, they lose seal and air from the choke (enrichener) air jet runs past the choke plungers and causes the engine to race. To check this out, jiggle your choke arm next time it happens; typically the idle will drop back down almost immediately until the plunger lose seal again.

wiredgeorge wrote:

The choke plungers are shot. When you are sitting there idling, they lose seal and air from the choke (enrichener) air jet runs past the choke plungers and causes the engine to race. To check this out, jiggle your choke arm next time it happens; typically the idle will drop back down almost immediately until the plunger lose seal again.

Is this something that can be repaired with the carbs still on the bike?

Nope. The carbs have to come off. You then have to remove the choke actuators and choke arm. At this point, it is easier, from my perspective, to disassemble the set and remove the plungers but it is possible to take a screwdriver and tap the 14mm plunger nut/base loose and unscrew them and pull them out without full disassembly. It requires a bit of skill to install new pads. Forum rules pretty much limit what I can say about the subject at this point. Sorry.

WG: Well believe it or not that occured to me also but I guess I needed to hear it from and expert. I noticed one of the plungers was really worn alot.

Do you have any idea where I could get the replacement parts?

You could PM me the info if need be.

Thanks,
Bob

I noticed one of the other vendors mentioned a service that they sell in one of the posts in an engine thread so I will just say that when we rebuild carbs, the plunger pads are replaced, as needed. We used to perform plunger pad replacement as a stand alone service but was a time eater for the return so we now only do it as part of a carb sale or rebuild service.

The alternative would be to try and buy another set of carbs and steal the plungers or try and find NOS plungers. I am not sure any other carb places replace pads or offer that service but you could certainly check around. Perhaps some of the places in the "Vendor directory" might be able to help.

Well WG, I think it would be nice of you if you tell me where to get them little rubber things on the end of the plunger. You must be able to get um...why not me?

Maybe you have the part number? Then I could do a search for them.

Thanks for your help,
Bob

Bob, The plunger pads were an integral part of the plunger and not a separate part; we manufacture them for our own use. You won't find them for sale, near as I know.