Really wierd misfiring/sputtering problem on KZ1000

Hi folks. Having an extremely wierd problem with my recently bought 94 KZ1000P (cop bike).

The bike misfires heavily (heavy coughing/spluttering) at low RPMs under moderate acceleration. With gentle acceleration from a stop it doesn't misfire, and it seems to run fine at cruising speeds on the highway (or maybe I'm not noticing the misfires at that time). Here's the wierd part: it continues to misfire in exactly the same way when running on three cylinders (any three, it doesn't matter which one I disconnect), but it *doesn't* misfire *at all* if I have only two cylinders connected (again, any two cylinders).

When I disconnect a wire, I "ground" it to the chassis with a spark tester, to ensure that the other cylinder on the same coil is getting a spark. I can disconnect any two cylinders-- on the same coil or on different coils, it doesn't matter. I don't get any coughing at all.

Some info on the bike. It's got a stock air filter and exhaust, stock coils, stock NGK BR8ES plugs gapped to the stock spec of .028. I am using car wires, which have about the same resistance as the stock wires (I also tested all 4 wires with a spark tester, and they are fine). The plugs show no detonation or preignition. Plugs 1 and 4 are just a tad on the rich side, while plugs 2 and 3 are definitely sooty (but again, I can ride the bike on just #2 and #3, and it doesn't miss). Let me know if I need to give more info.

So I'm puzzled. Can anyone tell me what's going on?

TIA!

The problem is very likely electrical. I suspect a weak spark is causing poor combustion. Go to the FILEBASE and read the article on "coil powering". It is the most frequently downloaded article. A precursor to doing this mod is to measure voltage at your coils. A very dirty air cleaner can also cause the sooting you describe as can using high octane gas (retards detonation and screws up combustion on a low compression engine like yours). If, after testing coil voltages, you have less than battery voltage at the coils, I suggest you perform the simple modification and report back. This discussion will likely end up in the "ELECTRICAL" section I suspect. Good luck.

there is a old saying that if it sounds like carburation it's electrical, and if it sounds like electrical it's carburation. could be a simple tuning problem. try new plugs, check sync of carbs, idle drop all 4 carbs.
by taking off the spark lead you are looking for a valve leaking compression. and if that does not identify the problem cylinder time to look elsewhere. (or maybe your points are out of adjustment )

Post edited by: trippivot, at: 2006/06/20 09:42

Excellent, thanks for the replies.

I have been putting in premium. I'll switch it to regular, hopefully that will help some things.

I'll also definitely try fitting a relay to the coil as suggested in the doc you pointed to. I didn't realize that the ground connection to the coil is the one that is flipped by the ignition system. This makes sense to me-- maybe the voltage drop on the coil primary leads is too high when feeding current to 3+ cylinders, but not quite high enough to cause a problem with only 2 cyliders.

About the points-- it's a breakerless ignition, so I guess perhaps the only thing that can go wrong there is the mechanical advance...unless the chips are broken. I don't think that's it, though, because the engine runs fine on 2 cylinders.

Before spending the time and effort on the relay mod, DO check the voltage at the coils... a 94 is kind of a big MAYBE age for a bike... 12 years old now so MAYBE it is having dirty connections, shakey kill switch or poor connections in the ignition switch. All depends on where and how the beast has been treated.

As far as gas goes, hi-test is a marketing hype adventure. The gas companies tell you it is "BETTER" than regular gas. Has wonderful additives to make your car (motorcycle) run more powerfully! Well, octane is there to keep gas from burning too early on higher compression engines. Your ol' cop bike is about 8.5:1 compression so you could probably burn kerosene hehe Seriously, the regular will burn hotter and keep the crud out of your combustion chamber.

Hey Trippivot... what did you mean about taking off the spark lead to look for a valve / no compression problem? You mean taking off the plug lead and no difference in the way the bike runs? You have me curious as you seem to know your stuff. Where did you pick up wrenching? Do you wrench for a living? Good stuff! Your avatar pic makes you look constipated but your background makes me think you are professional? Bwhahaha Cheers!

I just tried the coil fix, but unfortunately it didn't work.

I didn't use a relay, I just hooked the coils straight to the battery as a test. It did make a difference in voltage--before the voltage at the coil primaries was about 11.8V, and it went up to 12.7V after I attached the new wires. But still, it didn't make a difference in this behavior--same type of missing. I disconnected the new wires afterward to avoid draining the battery.

Strange problem. I guess there's one more thing worth trying-- fill the tank with regular, and drop in new plugs, while running with the new coil primary wires. But, I'm not too hopeful.

Anything else it could be?

Of course there is more to check, it ain't fixed yet is it! I had a very similar experience with the coil mod

Do you have a manual? I suggest looking in the clymers manual and fully testing the ignition, there are plenty of things that can go wrong there.

How many miles on your beast?

I do have a transistorized ignition, so I think the only thing that can really go wrong in a "sometimes" way is the mechanical advance. Would you agree? I have measured the resistance on the coils, and the wires/plugs are fine. Since the IC ignitor is under the same load whether it's 2 cylinders or 4...doesn't seem like it would cause this problem. But it's worth a check. After I get the cleaned carbs back on.

BTW, it has 65K miles. But it's a cop bike, so it has had valve adjustments and the rest of the maintenance done on it religiously.

The funny thing is, I used to have an old yamaha 600 sportbike. That thing was inferior to kawasakis in all respects, except for one thing. I treated it like complete dirt, didn't do a single bit of maintenance on it for the 6 years I owned it except swapping batteries when the bike wouldn't start. I mean, not even oil changes. I certainly didn't touch the carbs at all. I would leave it sitting for months, and once for years. No cover, nothing-- sat out in the rain and snow. But it would start right up after a battery swap, and run just as well as it always did. I only rode it 3-4K miles total, but now looking back I'm amazed I didn't have any carb troubles like I'm having now.