4000 high idle! Need advice

Ive rebuilt the carrbs already to make sure the needle jets aren't sticking and my throttle cables dont hang up. This is how it goes... I start the bike and she has a rough idle for awhile then smooths out then when I roll back on the throttle it can quickly climb to 4000 and stay there till i turn down the idle screw then when it comes down i turn it up to like 1030... around there and it settles till i roll on the throttle agen. then when i ride it stays at 4000 even without the throttle. Does anyone out there have a clue of whats going on with my carbs? And I already covered the vacuum leak aspect

By the way, I took of the wind jammer to get a more natural look on my bike!

PUT YOUR BIKE YEAR/MODEL IN YOUR SIGNATURE. You might also want to put your location in your signature in the even local help is available.

In general, I can't off specific help as I don't know whta type carbs are being discussed. In general, there are two reasons the idle will be erratic as described. Tight throttle cable(s) or air leak in the pilot circuit (or choke circuit).

looks like 24s or maybe 26s from the picture.with the bike shut off crack throttle all the way open and release real fast.does it come all the way back?

i already checked the reurn on the cable and I did the choke test to check on the leaking circuit. I have a kz650sr 1978 with mikuni carbs with the accelerator pump. But i might have that vacuum leak i havent gotten to yet. I have one hose where i can feel the vacuum sucking in then theres a next hose that i dont feel any thing at and i just plugged those hoses onto these sticking out parts on the carbs, so i just have to get reliable caps for them. Plus i just fixed that oil leak I had at the shift components coverI still waiting to see long term results, cause i still have oil around the area...

First of all, perhaps you don't understand WHY a cable can make the idle hang. If it is too tight, it will hang. Make SURE you see visible slack in both throttle cables. To put some slack in the cable, loosen the locknut on the barrel adjuster on the right hand switchgear (throttle cable actually). Turn the barrel towards you as you view the cable end that goes into the carburetor assembly. You should see a bit of slack.

Next step is to view my web page "VM Carb Connections" document and make sure the carbs are hooked up correctly.

If the idle still hangs, you have an air leak in either the pilot or choke circuits. You say you have checked the choke circuit somehow. How was that done? If done correctly, that would then point problem resolution to the pilot circuit. Please try the other things first and get back if they don't fix the problem.

I will take your advice very seriously Wired. The choke test i read in another posting where you wiggle the choke lever up and down and well as soon as i turn off the choke the idle goes down and raises as I turn it back on so i dont see a problem there, plus I will look at my cables again, but the teacher at my school saw no problem and hes experienced in these bikes also, so he saw no problem there. Plus I get that spitting coming through the vacuum line. Is that a serious problem?

Also would the pilot cicuit involve the pilot jet which controls the idle along with valve seat(the small spring thing that controls the float. Does that loose its spring tension after awhile or wear out? cause I dont know I checked those too and they do seemed fine to me

kzwolfsr wrote:

...i just plugged those hoses onto these sticking out parts on the carbs, so i just have to get reliable caps for them.

I had a VERY similair problem with my 78 KZ650. On the carb rail are three rubber hose ports. One, which is on the carb for cylinder #3 (I think it's #3) is for the gas petcock. The other two 'vent' the carbs. I had capped these off and had the problem you describe. Not knowing, I tried connecting a hose between the two (which still does not VENT the carbs) and I had the same problem. Trip to the local Kawasaki shop to talk to a knowledgable mechanic. Those two ports are supposed to have a hose hooked to them that is routed up under the tank and then left open. They allow air to vent into the carb chambers. Without them, a slight vacuum will develop that will suck gas through the main jet.
Another thing, With the carb vent ports capped off, when I took off a vacuum cap on one of the intake manifolds to attach a vacuum gauge, a little bit of gas would drip out. After I let them vent, that stopped.

That's my experience. Drove me crazy trying to figure it out. I think I must have disassemblied and cleaned the carbs and rail three times.

Once I corrected this problem, my engine behaved. And, having spotlessly cleaned carbs runs really nicely. Until my coils crashed.... It's always something!

Good Luck.

I don't know your teacher and while it is good to have respect for your teacher, I would still take a look at my own throttle cable if the bike's idle is hanging. It has been my experience that while I value ALL sincere advice, using my own senses, experience and eyes while keeping the advice in mind, is the best way to resolve any problem.

I suggested several areas to explore. The EASIEST is the throttle cable. You can look down and see if there is some visible slack. If the cable is perfectly straight in the holder, it is too tight.

View the carburetor connections page on my website. The plugs on your carb holders must be in place and must be NOT CRACKED. Some bikes use a vacuum actuated petcock. Vacuum is supplied to the petcock via a hose to the carb assembly. I don't know if yours has a spigot or does not but the connections page on my web site shows how this spigot should be connected. It can NOT be left open to the air... big air leak otherwise.

Last, where are your pilot mixture screws? They will be either on the sides facing the outside of the bike or on the bottom in front of the float bowl. Both types of screws have orings that if deteriorated, will cause extremely erratic idle.

Since you have already done the choke plunger seal check, this is likely not the cause for your idle issues.

hey man I checked out your site on the page connecting mikuni vm carburetors and I instantly saw my problem. I have the vacuum hose off and just plugged onto something on my carb, just to plug it, and the vent line plugged into the gas tank where the vacuum line is supposed to go. Big thanks man!!! I cant wait to see what will happen now

Good deal! Let us know how it turns out...