KZ650 rough idle, hunting, pop and dies when hot

My KZ650B is not idling well when hot. Today it actually died twice while waiting at a red light. The bike starts on one kick, seems to idle smoothly when cold, but will start to stumble a bit when hot, idle high and low, and occasionally a pop can be heard. This might be a carb pop, but it also sounds a bit metallic like a snap or a zap. Sometimes the bike will pop and the idle will recover. Occasionally it will pop and die.

I've tried spraying carb cleaner near the carb holders, and can't get a response.
I'm having a hard time determining if this is carb, electrical or engine related.
The fuel level might be low by a mm, 2mm at most and the jets are clean.
The coils are new and the battery is charged. The valve clearances are good.

One other thing I noticed is that the bike didn't seem respond much to the air screws.

What do I check, or re-check next?

It could be as simple as a rich mixture. A rich mixture will work well when cold but cause problems once you're at running temperature.

After running it for a while without the choke, stop the engine and check the spark plug. It should be clean-ish and brown. If it's white, you're running lean. If it's black and sooty, running rich. While you're at it you can check the spark plug gap, as that could be it too.

Once again I'm going to ask. When was the last time the valves were adjusted? If too tight it will act like that.
Steve

My plugs are black, and have not changed much since I cleaned the carbs, adjusted the fuel/float level and checked the float valves.
I'll check the gaps, but I recall they were correct.

I've got a chopped exhaust (that might not be from a KZ650), it's missing the cross piece between the sides.
Cheapo pod filters, 15 pilots, 107.5 mains with needle cir clip third(middle) position.
My float needles have very slight wear, 3 are 2.0 and 1 is 2.5.
Fuel level is maybe a mm or so low last time I checked.

I haven't adjusted the valves. They varied from 0.10 to 0.15mm (4 to 6 mil)

If your plugs are black, then you are running rich, so you will need to fix that, even if just to rule the problem out (although it probably is the problem If you've changed the exhaust and filter it's not unreasonable to think that's changed the mixture.

Those valve clearances are perfectly fine.

You state that the plugs are black. Assuming it's soot rather than oil, I strongly suspect the problem is jetting. If someone cut the exhaust system up and put pods on the bike it is highly likely they did not find the magic formula for jet sizes when fiddling with the carbs, and as a result the air/fuel mixture is too rich. Ed

Maybe try lowering the needle to the bottom see if it makes any difference?

Were fuel levels checked via clear tube tests?

Good Fortune!

cjaldous wrote: . . . Cheapo pod filters . . . .

Reportedly, some pod filters may block the carb's pilot air entrance.

Could test run without the pods to determine whether there's any change in lower rpm performance.

Good Fortune!

Is the advancer unit lubed and properly functioning?

If not already done, would assure that the advancer unit is properly functioning by viewing its operation under a timing light while watching it move quickly back and forth as rpm is varied by blipping the throttle.

Good Fortune!

Lack of response to pilot air screw adjustments indicates something is wrong inside the carb, usually an obstructed pilot circuit.




Entrance to the #2 pilot air passage is the area subject to being sometimes obstructed by a pod filter.

Good Fortune!

Spray carb cleaner and lots of compressed air through the air passages like Patton says, adv and pods check too and the clip should be in the 4th slot second from the bottom stock so maybe even the 5th like Tyrell says........ a 15 pilot and 107.5s for pods and cut up pipes is no way too rich either I would think......... probably a 2.0 nettle for that 4th carb too.