Kz550 idle/run issue

Hi all, great fourm here.

I’ve recently picked up a 1981 kz550a in pretty good condition but hasn’t run in 10 years . Fuel system was very clean. Fixed various problems, bike ran pretty good with stock pipes and no air box . Installed a kerker and pods, tuned it with dynojet kit. Got it damn close first try but here’s the problem.
It will start and run on the kickstand but when the bike is stood up it’ll start to run lousy and drop cylinders. Back on kickstand or just lean bike in same direction- bike starts runs great and will happily ide smoothly there.
Sooooo I figured float height. Went 3mm either way on float height, no bueno. Same deal. Went into petcock and pulled the o ring and spring thinking maybe problem is there. Nope.

So now I’m stumped, any suggestions? Thanks

Check the factory service manual for the fuel level spec, and set the floats to that height. That should get you in the range for that.

What do the plugs look like? That will tell you a lot about whether the engine is rich or lean. Best to use new plugs, as they'll show the most accurate readings.

EDIT: I'd also double check that the throttle cable has a bit of play, with the bike on both the stand and stood upright. It could be that the throttle is being held open a bit if the cable is routed incorrectly, and that's what's causing it to run well leaned over while not running well upright.

How much fuel is in the tank? If very little, was the petcock set to reserve?

That could be many things. Since you probably had the tank off, I would check the wires around the tank and frame there.

If its a fuel flow issue, did you add a filter? Some car filters wont flow enough with just gravity.

Ok so I pulled the tank and rechecked all electrical under there, everything looks good. Made up a alternate fuel supply and ran it without tank. Same issue. I also ran it out of gas while tilting and straightening the bike and the symptoms continued till it ran out of gas. Gonna use the clear hose method to look at float levels tonight. I’ll update here

kickstand switch?

Doesn’t have kickstand switch.

Most 550's don't have the sidestand switch. Some of the later ones do, but they don't affect the ignition, they only activate a warning light. The Zx550A has a sidestand switch which kills the motor through a diode circuit.

Only a low fuel level in the carb bowl cause the idle/run issue if the bike is on the sidestand. A sidestand switch failure would switch off the ignition immediately.

Scirocco wrote: Only a low fuel level in the carb bowl cause the idle/run issue if the bike is on the sidestand. A sidestand switch failure would switch off the ignition immediately.

Not necessarily. An intermittent electrical connection can cause some very erratic behavior. You are assuming a properly functioning system. I am envisioning some of the twisted together, greasy, smashed and otherwise neglected components that I deal with quite often.

Of course the fuel issue is the most likely cause, but I seem to remember a thread a while back that turned out to be a bad connection under the tank, on a bike that EVERYTHING checked out A-OK. :S

If the bike is in neutral, and the neutral switch is good, then the sidestand switch won't matter. Of course, the neutral switch could be flakey too.

Either way, it's not a feature on the 1981 Kz550A2, so it's not a consideration. It could still be electrical, but it won't be the neutral switch or a sidestand.

loudhvx wrote: If the bike is in neutral, and the neutral switch is good, then the sidestand switch won't matter. Of course, the neutral switch could be flakey too.

Either way, it's not a feature on the 1981 Kz550A2, so it's not a consideration. It could still be electrical, but it won't be the neutral switch or a sidestand.

And once again that would be the proper operation. Of course something is not operating properly in the absence of a side-stand switch, be it electrical or fuel related. or the OP would not be posting questions to the forum.

Whatdya think? .. my headlight is not working, and my oil light is not working.. What's wrong? :blink: