Erratic idle on KZ1000

I have a 77 KZ1000 A1 and the idle is giving me hell. It is either stalling or sounding like an old chaff cutter or it is racing between 2500-3000 rpm. It holds it's revs during gear changes and there is no engine braking due to the high revving. It looks like the carbs are not the originals as these have an air screw instead of a pilot mixture screw.
the bike is fitted with pods and a 4-1 V&H. The main jets are 120, pilots are 17.5 and the needle has been raised one position. I have recently had the cylinders honed and new rings fitted and an O ring set fitted to the carbs. Yesterday I pulled the carbs and found 3 of the pilot jets blocked, I recently put some fuel system cleaner in the tank, both fuel lines from the tank have in line filters.
I did the valve clearances last week and all are within spec. The timing is correct, (it is a Dyno III system with Dyno coils.
Having done a search on the forum for these symptoms it is pointing to an air leak somewhere. I sprayed the rubber manifolds and carbs with RP7 while it was running but did not pick up any change in running, any ideas of what I should be looking at next, regards Neil

Did it always do this or did it suddenly come on? Also check the timing advancer behind the points. They will get sticky and give you the same symptoms.

This came on all of a sudden, I did the advance mechanism when I adjusted the shims for the valve gap about a week ago. My timing light had blown a globe so I set the timing with the static method. Thanks for the suggestions, this is realy getting to me as the weather is absolutely perfect for a ride, the bikes will be out in full force today, regards Neil

3cav84a wrote: This came on all of a sudden, I did the advance mechanism when I adjusted the shims for the valve gap about a week ago. My timing light had blown a globe so I set the timing with the static method. Thanks for the suggestions, this is realy getting to me as the weather is absolutely perfect for a ride, the bikes will be out in full force today, regards Neil

I have been told that exact symptom -- 'funky idle' can be caused by one or more missing part #32 in this diagram -- it's a rubber o-ring that slips onto the pilot adjustment screw (part #31 is the pilot adjustment screw):




The symptoms I was told were: "sometimes the idle seems fine, other times it's erratic, it will rev high, or it won't idle at all" sounds like what you have.

Me personally? I used to think "the dang orings there are so tiny, if I lose one or all of them big deal, surely they're 100% unimportant, they're too small to be needed. "


So luckily I've always been careful during carb cleans/rebuilds to honor the parts diagram and adhere to it, mainly because I'm an anal sumbidge. So I've never had a need to troubleshoot this problem as being due to missing or old/damaged pilot o-rings.

But seeing as how you have the idle symptoms he spoke of, a question for you is, that diagram above is for the 1977 Kz1000-A model, do you have those carbs and/or does the carb set you have need those rubber orings on the pilot screw there?

The bike is a 77 KZ1000, year of manufacture is 12/76 but the carbs are not as you pictured, mine have an air screw coming in from the side on the air cleaner side of the carb. I just took it for a ride and it is just as erratic. I think I might try taking the air screws out to about 2 1/2 turns and maybe drop the needle back to it's original position.

A pic of the carbs at hand would help i.d. them.

Perhaps they are smoothbores?





Good Fortune!

I have tried several times to upload a picture of the carbs with nil result, will keep trying as tomorrow is going to be a great riding day again.

Do the carbs at hand match the pic of the smoothbore as posted earlier?




What browser is being used?

If using latest version of Firefox, could try a different browser.
Lastest versions of Firefox were recently unable to post pics, but I don't know whether the issue has yet been resolved.

Good Fortune!

Stock carbs on the 1976 KZ900 were also 26mm Mikuni manual slide carbs, but with the side-located pilot air screw.

Note also the side-located float bowl drain screw.
And the overflow nipple from bottom of float bowl.





Good Fortune!

3cav84a wrote: The bike is a 77 KZ1000, year of manufacture is 12/76 but the carbs are not as you pictured, mine have an air screw coming in from the side on the air cleaner side of the carb. I just took it for a ride and it is just as erratic. I think I might try taking the air screws out to about 2 1/2 turns and maybe drop the needle back to it's original position.

Another easy check. On the intake manifolds (the black rubber parts that connect the front of the carb to the engine) there should be a capped-off vent on each manifold, as shown here:

THIS IS A PICTURE OF A SET OF 4 Kz1000 INTAKE MANIFOLDS:


If you notice, there are plugged-off ports that stick out from each rubber manifold. In the photo, those ports are capped by rubber covers that look like a big rubber bullet.

An easy thing to check -- make sure

1) each of your intake manifolds has a port that is capped because otherwise air will get sucked into the engine on that cylinder, wreaking havoc with the RPMs of that cylinder

2) now, after verifying all four intake manifolds are properly capped off -- CHECK THE CONDITION OF THE CAPS. If they're dilapidated and not capping the port off completely, air will get sucked into that port, messing with the running of that cylinder.

Those capped-off ports are used to adjust the carbs -- unless you're doing a carb adjustment, those ports sticking outward from each manifold *must* be capped off and closed.

If one of those ports is open, it will 100% screw up the idle and the affected cylinder can race up in RPMs due to the air leak at that port.

That looks very much like the carbs I have on the bike, the overflow tube is the same as is the drain screw. The air screw is the same as well. Also another difference is once the top of the carb is removed to sink the carbs besides the locknut and screw there is another screw next to it with lock tabs securing it.
Patton yes I am using the latest version of Firefox so I will try another one regards Neil

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.