Two issues with my 82 KZ750 LTD 4cyl

I've risen this bike for maybe 4 seasons now, this summer being the 5th.

Last year I had two issues develop and I'm not sure how to diagnose them.

I don't think they are related but I guess they could be.

Issue 1: once I've ridden for 10-20 minutes, the bike loses power like its running on 3 cylinders or something. If I just hold the throttle steady it will usually maintain speed, and then power will come back for a second and back off. It does this a few times, then suddenly it comes back like it wants to throw me off the back. Then even if I ride for an hour or more, it won't do it again. Usually if I ride again later in the day or early the next day it won't do it. But if I don't ride for a couple days, I have to go through this again.

Issue 2: if I am accelerating it's fine, but if I am trying to maintain an even speed, I'll hear a noise. The only way I can describe it here is the sound your mouth makes when teaching a child the sound for the letter T.

Issue 1: check your spark plugs color to get a first impression of the engine condition.



Issue 2: make a short video of your running engine and upload it here

Get repair manual

www.750turbo.com/manuals/GPz750_Base%20Manual.pdf

Check for intake air leaks when the engine is cold. Spray carb cleaner, wd-40, even silicone works, spray down all joints and vacuum lines and plugs and listen for any change in rpm.
If one cylinders plug is different color really check that cylinder well for air leaks.

Had an old gs that would leak air at the boots when cold, then as it heated up it would seal a bit better. Cold days it took longer than hot days just felt like it was super cold blooded if I ran with slight choke on it was good thats how I finally tracked it to air leak while cold.
It took me a long time to find it, I thought it was electrical...Changed the boots fixed the problem.

I had an intermittent firing problem from poor spark plug wire connections. If the plug wires are old old old, replace them with 7mm copper core. You could try de-doing the connections. unscrew the ribbed compression boots at the coils & untwist the wires from the spark plug caps. the wire gets oxidized over time, so nip off the ends a tad. or go ahead & get new. If needed, you may be able to reuse the outer sheathing from the stock plug wires so that the new plug wire fits right. silicone spray would help in removing the sheathing.

Make certain the battery is good. the bike needs a good, fully charged battery to run right.
I do a high beam load test and use a Ctek US 0.8 smart charger & VC97 digital multimeter.

Issue 2 could be normal valve ticking. not to be overlooked, though, is the valve clearance check. the check is fairly straight-forward. changing shims is more work, but should be do-able. the valve clearance procedure in the manual doesn't mention the tensioner. so either lock it beforehand, or reset it when done checking.

It's difficult to trace running problems on a 35+ year old bike unless all the basic maintenance tasks are up to date. Number one on the list of things to do is to clean the carbs and make sure the tank is clean, and number 2 is to adjust the valves.

After you take care of these things move on to what martin suggests and work on the ignition system. What you describe sounds like a cylinder dropping out and that could well be caused by intermittent firing of one or more cylinders. There could be poor electrical contact somewhere in the ignition circuit or maybe even the ignitor is bad. Cleaning the connections should be part of your basic maintenance work.

One other possibility is poor petcock flow and/or a plugged up fuel cap vent system thus leading to fuel starving the carbs.

Good luck

I had changed the throttle cable last year, so I thought maybe I ripped a boot when i removed the carbs. I sprayed starter fluid all around while the engine was running. No change in rpm.
I took pictures of the plugs, but I can't get my photobucket working to post them.

I do have a plug wire with damaged insulation. It was taped up, but I figure ill change them anyway.

I checked the return spring on the factory electronic ignition, it seems ok.

I took pictures of the plugs, but I can't get my photobucket working to post them.

I now use imgur.com. .... not sure if it's me or what, but I've had trouble with photobucket & the ads there kinda drive me crazy at times.

Ill look at imgur.

I contacted z1 about coil wires. They are suggesting Dyna suppression wires because of my factory electronic pickup ignition instead of points.
Is that right? I thought the suppressing wires were only for true aftermarket electronic ignition like dyna S.

My current wires are yellow NGK with screw on coil ends.