Erratic idle on KZ1000

3cav84a wrote: So I finally was able to upload a picture of the carb,I pulled them out again and lowered the float level on each of them, same result. It is now showing a pattern whereas when I start it the bike will idle on about 1000 rpm and sit there all day so long as I don't touch the throttle but as soon as I wind up the rpm it will sit an about 2500-3000 rpm until I turn the ignition off. I think I will have to swallow my pride and take it to a bike mechanic as it has totally beat me. 5 days working on it and no results, I have better things to do.

You have (may have) an air leak. However, first, a couple other things that can create high idle is

- the choke is on -- turn your choke on and off while watching the 4 carbs so you can discover the part on each carb that moves when the choke is turned on and off. Then make sure that when you turn the choke off, each carb's choke does in fact close, ie. you don't have one carb's choke sticking on

- the large round idle adjustment screw knob needs to be adjusted -- you owe it to yourself to at least try that one -- find out where that big round idle adjustment knob is on your set of carbs and when the bike does rev up to 2500-3000, try lowering the idle by turning that idle adjustment knob. Sometimes when we rebuild carbs that large round idle adjust wheel gets bumped and raises the idle.


One of the main symptoms of an air leak is an idle that will not settle down.


Could be:

1) one of those rubber plugs on one of the intake manifolds (see my earlier post with photo of the 4 carb intakes) -- one of the rubber plugs is missing or cracked/broken allowing air to get in at that point -- that cannot be allowed, that port is for hooking up a carb adjustment meter

2) a cracked, old and dried-out intake manifold -- if you pull the carbs and then remove the intake manifolds you can check for cracks/leaks -- if the manifolds are old and hard, they might leak

An air leak has as a symptom an idle that will not 'settle down.'

probably an air leak ,but....... :ohmy: just to throw this out there. :blink: idle speed knob adjusted correctly.
Check throttle cables as they need slack to work properly. :huh: are they too tight since you removed and reinstalled the carbs? :blush: it's supposed to have 2 to 3 mm throttle grip play. hth

3cav84a wrote: ... when I start it the bike will idle on about 1000 rpm and sit there all day so long as I don't touch the throttle but as soon as I wind up the rpm it will sit an about 2500-3000 rpm until I turn the ignition off....

During the racing idle, could try pushing the throttle closed by hand at the carb end, to see whether or not racing idle persists.

Could disconnect throttle cables at carb end -- needle-nose pliers may prove helpful -- then increase throttle manually by hand, with throttle cables disconnected, allowing the carb spring to pull the throttle closed (free of any resistance involving throttle cables) .

Either test could help diagnose whether or not a maladjusted or hanging throttle cable is causing the racing idle.

Good Fortune!

So today I ran the bike with the throttle cables disconnected, for the same result. I pulled the rubber manifolds off for a thorough inspection, they appear OK with no cracks, I have ordered a new set so that I can cut them out of the equation.
There is now a distinct pattern of clues developed.
Here is a rundown:
Start bike from cold needs choke
Bike is soon able to go off choke with the idle rpm at about 1000 rpm.
let bike warm up 3-4 minutes still at around 1000 rpm.
operate throttle so bike goes to 2000-2500 rpm and bike will hang there until I switch it off at ignition.
Immediately start bike and it is back to normal idle. The more I think about it I think the problem is not carbs or air getting in. I am thinking the springs on the centrifugal advance mechanism have weakened, all of the above clues tell me the advance mechanism is staying in the advanced position even though I have shut the throttle off.
I don't know if you can just buy the springs or if you have to buy the whole mechanism but I am really hoping that this might be the cure, if not you may send cards and letters to me Neil Holbrook care of the Adelaide Institute for the mentally insane LOL :woohoo:

Pivot points may be lubed by access through the timing window. But may do a more thorough inspection and servicing (clean and lube) by removing the advancer.

Good Fortune!

if the rubber is bad on the choke plungers it can cause the same thing.

G'day, I finally got a result, nothing wrong with the carbs although after all the stripping and cleaning I can do it in my sleep with my eyes closed.
Today I worked on my theory about the centrifugal advance mechanism hanging in the advanced position due to weak springs. I removed the springs and squeezed them together in a vice and got them red hot in a gas flame, I let them cool naturally without putting them in water replaced the springs and the bike has been running as it should do. I would suggest that eventually the springs will go weak again but by that time I should have a new advance mechanism installed.
Thanks to all who contributed suggestions as a result I am getting new inlet manifolds with new clamps.
I know that this was a strange one with all the indicators leading to an air leak but it was not until I really studied the symptoms that I decided to look at the springs, apparently a rare condition but it goes to prove you can't disregard anything, cheers Neil

Sounds to me like you have an intake leak I had that problem and it was because the silicone I used was permiable to gas . The best thing I found is 3m weather strip silicone if you take the boots off apply a bead of it and allow it to set up the apply another bead before installation and let it set a few hours best over nite it works greats I had that problem with an on Yamaha I had . Give it a try and best of luck