89 KZ1000P cutting out at high RPM

In the fall, on the Turnpike on my way back from a nice ride in Arkansas, my KZ1000P started intermittently losing power. I pulled over and let her idle, no problem. I rev her up whilst in neutral, no problem. I get back on and as soon as I get her in the road above 3,000 rpm, the same thing starts happening. As she loses power, the tachometer needle increases. I first thought it was severe clutch slip (bike has 36k miles) so changed the clutch disks, same issue. I then changed the coils, same issue. I then changed the spark plug caps, same issue. Could this be a bad igniter? Some threads suggest fuel starvation at higher rpm, but bike was running just fine all through the rpm range before this happened, so I think it is an electrical issue. HELP!

You mention that the engine rpm increases while the bike’s speed decreases. To me that sounds like the engine is not the problem.

When the clutch is not slipping here is a specific ratio between the engine rpm and the rear wheel rpm for each transmission gear. Consider the fact that when the clutch is not slipping the rpm of the engine sprocket is directly related to the rpm of the crankshaft through the transmission. The chain connects the engine sprocket to the rear sprocket so there is zero opportunity there for slippage there, and the rear sprocket connects directly to the rear wheel so there is zero opportunity there for slippage.

So how can the engine rpm rise without increasing the rear wheel speed? I only can think of two possibilities.

1 – Possibly the engine sprocket nut is loose and the engine sprocket is slipping on the output shaft. However, this problem would very quickly result in a major problem and would be very noticeable at all engine rpm. I seriously doubt this is the problem because the bike would not function well at any speed.

2 – The clutch is slipping. This is by far the most likely cause of the problem you describe. If the clutch is not adjusted properly, if it is damaged due to wear or due to the wrong motor oil being used, it can slip at higher speeds even though the slippage may not occur or be noticeable at low speeds. This is because there is considerable less stress on the clutch when riding at low speeds compared to riding at high speeds.

I understand that you believe the clutch is not the problem, but I respectfully suggest you take more time to ensure that the clutch cable is properly adjusted at all adjustment points, that the clutch springs are tightened properly, that the clutch plates are in good condition and installed properly, and that the correct motor oil is used.

Ed

Thanks Ed. I always use the correct motor oil. I did an oil and filter change when I bought the bike, and have done less than 1000 miles, before changing the clutch disks and changing the oil and filter again, I have been through the tensioner on the left side, under the cover and the issue is exactly the same as before. I actually think that the engine rpm is dropping during these episodes, but for some reason the Needle on the tachometer deflects quickly to the right. The other reason I don’t think it is the clutch is that no matter how hard I push the clutch ar lower rpm, the issue never, ever happens, only above 3,000rpm. Is there any additional jetting in the carbs that kicks in over 3000rpm that could be blocked? Any idea if the ignitor is prone to damage?

Electric or mechanical tach?


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I actually didn’t check, is an 89 KZ1000P, just assumed it would be mechanical, but didn’t check. Will research tomorrow.

99 percent sure its electric. My 83 KZ1100 is electrical.

If electronic, what does the behavior of the needle tell me?

Could be somethings wrong with the ignition.
Steve

Steve, any more specific ideas on the ignition? After replacing plugs, caps, wires and coils, I am kinda stumped, which is why I raised the potential issue of the ignitor, but which to buy new would cost more than I paid for the bike!

Nebr Rex asked the question that was in my mind as I starting reading the thread. Use your wiring diagrams to follow the wire that feeds the tach the signal and trace backwards. I'd look for any possible shorts in that wire as well as what component it comes from.

Was getting a tire repaired (roofing nail....as it turns out) this morning and whilst there, asked mechanics what they thought the issue was, 3 of them agreed that this was classic case of failed ignitor. The reason it works up to 3000 rpm and then fails is because that is the point the ignitor is supposed to kick in with another map. So, old one out and new (after market) module on order from eBay. Will update next weekend after install. Fingers crossed!

May want to check and service the mechanical advance if that hasn't been done in a while.