Won't Idle on all four - HELP!!! About to give up!!!

Okay, so, with the help of reading a lot of posts on these boards and asking few questions myself, I have gotten my '80 KZ550c to the point that it runs and rides under it's own power once again. But now I have come across a very strange problem.

I just finished syncing the carbs (With a Mercury style meter) and, while everything else looks good, I have the strangest inconsistant idle. If you start the bike and let it run, it will run just fine. No problems. Even with the ocational rev, it goes back to a normal idle. BUT, as soon as the bike is physically moved; picking it up off the side stand, sitting on the bike, bouncing on the bike (I kid you not), the idle jumps about 1-2000 RPMs. I don't know the exact RPMs that it hits or the amount that it jumps as the tach cable is broken. I never noticed it doing this before, but I also havn't been riding it much do it needing work (The bike has yet to see the outside of my neighborhood without being on a trailer). What could possibly be causing this to happen?

The bike is running lean, if that's a clue to anyone. I am running pods rather than an airbox due to the airbox being MIA when I bought the bike (Exauhst is stock). Would this lean condition be part of the problem? Why would the idle be effected by physical movement of the bike?

Post edited by: KB02, at: 2006/09/19 09:10

Post edited by: KB02, at: 2006/09/27 11:53

is the throttle cable binding?

Nope. That was the first thing that I thought of, too. It's all free and clear.

vacuum leaks? cracked carb boots?

The carb boots are fine. While vacume leaks have been plauging me in the past on this, I thought that had them all fixed. If it is a vacume leak, I can't think of where else to look for one. And why would it be effected by physical movement of the bike?

Could it be a float bowl that's too full and when I move the bike it spills extra gas into the engine?

when you did all the stuff to the carbs , was it on the center stand? just wondering about the float levels/carb adjustments

yes, the bike was on center stand. The float hieght on #3 was a little bit high, if I remember correctly.

That brings up another question. When I was balancing the carbs, #3 was my biggest problem. I was using a mercury meter and while #'s 1, 2 and 4 were pulling at about 24-26 on the meter, #3 was haning out at around 16-18.I could not adjust #3 any higher than that. It was at the end of the adjustment range. What I ended up doing was dropping the other three down to meet #3. The result was a much smoother idle, untill the bike was moved. That's when I became really confused

I had bench synced the carbs before putting them on the bike.

Also, I was using the vacume nipple that is in the rubber intake boot between the carb and engine. Is that the right place to put it? I can't find any help in my clymer's manual and I can find no other spot for it.

Okay, so float hieghts are all fine and consistant across the board. I did notice that I had one coil connection that was very loose. I practically fell off while I was taking the coils off. (engine is now sitting on a stand on my Garage floor). I lso noticed that when I took off the throttle close cable, I heard what sounded like the throttle slamming shut. I'm pretty sure there was slack on the line, but I guess there was a possibility that it wasn't.

SO, here's my new theory:
The engine, while sounding a little rough at idle (really sounded fine, just a touch rough. I never thought anything of it) it was only running on two cylinders. While shaking the bike, the connection was made for that coil and, with the throttle at a bit of a pull from the close cable, it reved up to what it was supposed to be. When connections was lost again, the bike dropped back down to the lower idle on just two jugs.

What do you all think? The engnine is currently out and getting ready to go off for a good clean up with glass beads while I give the frame a good scrub down. Let me know what you think and I'll let you know what I find when I throw everyting back together.

Okay, forget my "New Theory" in that last post. It's garbage.

Sorry to bring up an old post, but I still need help on this one.

So the engine is back from the cleaners. It is back in the bike everything is connected, Electrical connectors on coils have all been replaced. Idle is still screwed up.

So here is the refined issue: The bike will not idle on all four cylinders. I am thinking, now, that it is only idling on three. Occationally you will here a pop of the forth kicking in. (you know what they say, three out of four ain't bad, which is why it doesn't sound awfull when idling, just a bit rough). Rev the bike and all four kick in without an issue. As the bike sits idling, if you physically move the bike, take it off the side stand, jump up and down on the seat, etc..., the forth cylnder will kick in and the bikes runs like it should for a second, then jumps back down to the rough idle.
I am not 100% positive, but I think it is Cylnder #4 that keeps cutting out on me.

The next time that I will have time to work on the bike will be thursday evening. Here is what am planning to do:
I am going to re-check compression on all four jugs.
I am going to re-synch the carbs.
Since it will occationally pop on the forth, I don't think I have any clogged jets, but should I ckeck the idle jets anyway?
What else should I be looking for?

definetly recheck the jets and float levels... the idle jet being partially clogged will bugger things up... make the synch hard to obtain..

Didn't see how your mixture screws were set.. but make sure to start from factory first and tweak it..

Its amazing once it runs on all 4 at idle.. its like the motor quiets down.. and says... ahhh!!!

sounds like an electrical issue like loose wire that makes a connection momentarily when you shake it.check all your plug wires to make sure they are connected.i had problems on a bike that would only run on 3 cylinders years ago .i pulled the carbs apart 3-4 times replaced the stock electronic ignition with a dyna 3 and still couldnt figure out why it wouldnt hit on all 4 till about 3500 ten it would pick up number 4 so hardheaded me decided to swap coils around ended up being plugwire broke internally but once it got above 3000 rpm it had enough fire to jump the gap and would run on all 4! :evil: so ya never know!

hey trav and tellie tubbie,i answered a question about a kz550:woohoo: :woohoo: :woohoo: :woohoo: :woohoo: :woohoo: and it feels great