engine not running smoothly on idling

Hi

I thought I had better start a new thread on this matter that drives me crazy.. I have already got som good thoughts from you, but now I have to revise the problem indications. The problems are not big, but enough to irritate me.

I have a kz650 -78. I put the choke up and starts the engine. It revs upp and I have to be very gentle and keep adjusting the choke a minute. Then I can lower it and the engine runs by itself. If I let the choke drop to early, the engine dies. After warming the bike up, I can drive the bike normally. This seems like a rather normal procedure.

Whats' not normal is that during start and warm up, one cylinder is running irregular. It also misfires (sounds like a sneeze). Or is it called backfiring? After a while all cylinders seems to go more regular. Still though, at idle, I notice that it jumps sometimes. No misfiring though, just a bit irregular. I tried to find out which cylinder, by taking off the spark plug cap, but I noticed a drop for everyone off. SO it's hard to tell exactly which cylinder it regards.

When taking the bike for a ride, it runs well on all cylinders. It feels really okej. No misfirning or so. The only thing is that when turning the throttle to fast, in the beginning of the throttle turn, it "bogs" down a bit (no power). If I start turning it slowly the first millimeters, it's then okej to turn it harder and faster. The engine responds. If I do it to fast in the beginning of the turn, while idling, the engine stops. This problem I think has to do with to much air. I have checked the inlet manifolders with start gas and w40, but there seems to be no leak. I also turned in the air screws a bit. From 1 1/4 (factory settings) to 1 turn out.

One strange thing is that the exhaust fume from one of the mufflers is colder than the other side. If one fume is lukewarm and more wet, the other feels cold and dry. All cylinders run. Could it have to do with the bike leaning towards one side, resting on the side stand? Or what? This surely indicates something!

Before I thought that the mixture was to lean to one cylinder, but when looking at the plugs now, all seem okej. Maybe a bit black sooty deposits, dry though. I also tested for air leaks.

What the hell is this? It doesn't seem to be any air leak, no faulty plugs. I don't feel like taking the engine apart and measure the valves this season, since it runs really okej when its warm. But this irregularity and misfiring at startup together with the bog down when turning the throttle to fast seems shouldn't be that hard to fix. And what about the different fume temperatures?

Looking for answers...:huh:

Martin

An intermittent problem like this can drive you crazy. I would change the spark plugs just to eliminate that. It sounds like a problem in the pilot jet circuit to me, but things like this can also be cause by a flaky plug wire.

I would also recommend having the carbs synchorized and make sure the fuel levels (float heights) are adjusted right.

Good luck.

Okej, thanks.

Any idea regarding the different fume temperatures?

And could the warmer fume from one of the mufflers indicates that the corresponding cylinders are overheated?

Or does the colder fume from the other muffler indicate that something is wrong with the corresponding cylinders, that they are to cold?


M

I had a similar problem. I went so far as to change coils with a known good set I already had...same problem.
I put a timing light on the spark plug wires and I could see which one one was firing intermittently.
The plug fired irregularly at warm up idle and bogged down when you would twist the throttle.

Replaced the spark plug...problem solved.

I have now discovered that one of the former owners of the bike has changed to a electronic ignition system.

Is there any way of checking/adjusting this?

M

Hello,have you checked the engine compression? Had a similar problem and it turned out that one cylinder had bad rings and low compression.

Bike runs well on the road. No misfiring or backfiring

Problem:
-misfire during startup (sneezing), then just a bit irregular idling
-different smoke temperature, lukewarm and cold (after startup during idling)
-bogs down when turning the throttle to fast during idling and on the road
-sooty dry plugs


So far:
-no air leak
-no faulty plugs
-previously changed to electronic ignition
-seemingly good engine power (responds well on the road)
-air adjustment didn't improve irregularity

And any idea about the different smoke temperatures (after startup during idling) from the two mufflers (lukewarm and cold)? I intend to see if its the same after running the bike on the road.

Turning the right carb screws in completely caused the engine to finally stop. Doing the same to the left carbs caused the engine to rund more badly, but it didn't stop.

I would like to make a compression test. Have to check the cost for doing it. I thought it was rather expensive. But maybe it's worth it. Then I would know if something is wrong inside. ANy way of doing a more simple one by myself?

Since I now have discovered that it has an electronic system, can you adjust this type of system? How do I check this type of system? Since it runs well when I am on the road and its warm, could it really be the ignition timing?

I was thinking of measuring the volt output from the coils. How do I do that? I lifted the plug hats off, but the bike responded with running badly, so I couldn't determine which cylinder it regards that way. Any other idea of how to determine which cylinder it regards, if the problem is the ignition parts.




M

I think your 78 has the same slide carbs as my 77. If so, then you need to understand:
- They're all cold natured. They just don't run well cold.
- Slide carbs lean out the mixture when opening the throttle quickly. So, bogging after quickly opening the throttle is just the nature of the beast.

Now, having said that, you still want to (and should be able to) have the bike accept throttle smoothly in the middle of a turn. My 77 runs pretty well so long as I'm smooth on the throttle. I've adjusted the air screws for optimum drivability. 1-3/4 turns out is where this occurs for me. At 2 turns out, the bike stumbles off idle. My bike is stock except for a Kerker 4 to 1 exhaust.

What is "slide" carbs?

Even when its warm it bogs down when I, on the road, go to fast in the throttle. But this only occurrs the first millimeters of the turnning. If I do that gently, I can than turn it quickly. The engine responds directly. I thinnk so anyway. Hav to try and do it really hard in the middle part. Maybe I have to live with it...

Any idea why the different temperatures on the smoke from each muffler?

And what about the misfiring during startup? I have a electronic ignition, so it should be no problems I thought.

M

Marp68 wrote:

And what about the misfiring during startup? I have a electronic ignition, so it should be no problems I thought.

M

That makes me think the pilot circuit is running too lean. can you apply a little choke and see if it runs better cold? If it does, that's a lean condition.

Marp68 wrote:

Even when its warm it bogs down when I, on the road, go to fast in the throttle. But this only occurrs the first millimeters of the turnning

On mine, that is caused by either the pilot system or the needle position. I had the same problem and fixed it with bigger pilot jets and moving the needle clips. YMMV

Marp68 wrote:

Any idea why the different temperatures on the smoke from each muffler

That makes me think one cylinder isn't firing as much which would account for why the exhaust for that set isn't as hot.

Another thing that can cause idle problems and run OK at higher revs is if the carbs are not synchronized. At idle, one of the butterflies may be closed and not giving one cylinder enough gas to run.

Marp68 wrote:

What is "slide" carbs?

I think that's the generic term for carbs that use the famous "SU" design which uses a moving piston with a needle attached to vary the fuel fed into the air stream of the throat.

The piston moves in response to changes in throttle position, when you snap the throttle open the piston jumps to open up the flow.

bemoore wrote:

I think your 78 has the same slide carbs as my 77. If so, then you need to understand:
- They're all cold natured. They just don't run well cold.

Good point. I have the BS38's on my 750 and even with them dialed in perfetly, I still have to use the choke to start and keep it running for the first couple of minutes. That's totally normal. It should run well when hot, but cold it has to have some choke.