81 KZ1000 doesn't go past 6000 RPM. Any ideas??

I bought a set of KZ Police carburetors for parts, and found that each slide diaphragm had small a hole in the side of the metal cylinder. When checking into what that hole was for, some tech at Vance & Hines thought it was there meant to be a limiter of some sort.
If your slides have the hole, it could be what your problem is...if not entirely, it may be contributing to it.

I modified the set of slides by painstakingly filling each with JB Weld, after running a tiny tap through each one to rough-up the hole perimeter for adhesion (see photo).
Those slides are exactly the same as the original ones to my BS34's (with that exception), and are now sitting in a box, waiting to be used again. The rubber diaphragms are in excellent condition, and the hole plugs held up very well, for the season I used them.




Send a PM if you would like more info.

What size fuel line are you running?
Also, when the tank is on, are there any kinks in the fuel line? ...even smaller-ish ones?

I like to check the simple things first...

Check your voltage regulator, it might be shot and the battery alone can't give enough juice to keep the coils going at high rpm.

Here is another update.

This bike is 81 and carb sliders didn't have that limiter feature yet. There are no holes at its sides, except the ones on the bottom.

I replaced 1/4" fuel line and filter with 3/8" ID, however it didn't make any difference.

As for the voltage regulator, I believe VR is working normally. Battery is charging fine, all lights work OK, voltage sensing line is within 0.5Vof the battery reading.

New 3.0 coils were installed. Still doing the same thing.

Dynajet recommended 165 main jets. I'm gonna go back to stock 122.5 and see if it affects.
If not, then will try different main jets that came with the rejet kit. (155,160 & 165)

Any comments or recommendations?

Is it for certain that the ignition coils are correctly wired?




Is the ignition timing owner-adjustable?

Good Fortune!

:huh: Any chance the cams may be off by a tooth?

Did you every resolve your issue with your bike not exceeding over 6000 rpm?

Any chance the cams may be off by a tooth?


THIS -

Kinda sounds like my 750 does the same at 8000 around 90+mph. Dont know since the gauge only goes to 85. But that's probably its limit.

I pushed the sliders up and blocked the air port, and the slides come down very slowly. takes about 40 seconds to fully down position. I think diaphragms are ok.

I put a few drops of engine oil on the slides, it should return sharper than that I'd say. Probably not your problem though as the vacuum lifts the slide but the spring returns it.

Those mechanical ATU advancers can be sticky and won't rev past about 6k, I know you said you are getting full advance at 3500 rpm. Are you sure your timing is right?

Have you checked your cam timing?
Steve

whirlwind598 wrote: Kinda sounds like my 750 does the same at 8000 around 90+mph. Dont know since the gauge only goes to 85. But that's probably its limit.

If your KZ750 is a 4 cylinder model (please add you bike's year & model to your signature line) I can personally attest that regardless of that NHTSA dictated speedometer the bike would exceed 120 mph when new. If yours won't go past 90 it needs work. Ed