Hi everyone
I've got a 1981 KZ440, and have fitted Mikuni VM-type round slide carbs, as the original carbs were damaged beyond repair. The air filter was missing, so it's running pods.
I've got a whole bunch of spare jets for these carbs, plus a Colourtune. So my plan was to get them working just well enough to begin the carb tuning process.
I've constructed a 1-into-2 split throttle cable using a dedicated kit. It definitely isn't catching anywhere.
The problem I've got is, I can get these carbs to idle and even to run, somewhat. But once the revs reach past, say, 3k or 4k rpm, it will hang. Then it will take a purposeful blip on the throttle to bring the engine back down to idle.
I've spent all day today, until well into evening, trying to chase down this problem. Here's what I've done:
1) I've made sure the throttle cable is completely smooth, with no kinks in it.
2) I've checked (by hand) that the slides open exactly when I begin to wind on the throttle.
3) I've set the (air side) mixture screw to 1 1/4 turns out, which I believe to be factory.
4) I've made sure the idle speed screw is set exactly the same on both carbs, by winding them both out until the screw was just touching the slides, and then out 1.5 turns.
5) I've made absolutely sure there is no vacuum leak.
I've checked all the above several times. I've opened up the throttle switchgear and inspected and lubed the throttle cable from there. I've also checked it at the 1-into-2 joining part. It's fine. The springs in each carb snap the slides down nicely.
My head is fixated on the idea that it's a carb imbalance problem, but with my best hand sensitivity I have adjusted these as finely as humanly possible so the slides begin to move up at the same time.
While inspecting other things, I came across what appears to be a semi-chewed wire going to the ignition points. Plus, I noted that I haven't yet checked that the automatic centrifugal ignition advancer is opening freely. Is it possible that the poor running could be down to one of these conditions and not a carb issue?
I know for a fact that the main jet in each carb is far too large, but at least they're the same size, and I was hoping this would give me a starting point.
Plus, the symptoms don't seem consistent with an excessively large main jet.
Could this be caused/helped by lowering the needles in the carbs? Perhaps they're simply getting too much air-fuel mixture all at once when the main jet circuits are active.
Any help/tips much appreciated.