Random power loss kz750-4

Ok so i searched but couldnt find related posts. Please point le to one if it exists.

Bike is a 1980 kz750 ltd 4 cyl
So over the past month i have been getting random power losses where the bike runs rough and will barely hold speed. It feels like its misfiring on one or two cylinders. It only starts to happen after i have had the bike running for at least 10 minutes or so. Its intermittent. I may lose power for like 10 seconds or for like 5 minutes. It comes and goes without warning. It happens in any gear at any rev at any speed wheather the engine is hot as heck or at normal running temps. I dont know what could have prompted this.

Heres what i did to try to fix it:
Replaced plugs with new ngk b8es, gapped to spec.
Went over plug wires to ensure good connections and clean contacts from coil to plug. Drained fuel tank looking for water or debris. None found.
I rebuilt the carbs about 3 months ago replacing almost everything and they are operating nicely, doubt they are the culprit. Had two solid months before this issue started. Replaced the timing advancer and battery just before doing carb.

Im thinking its related to the coils, maybe one is bad causing 2 cyl to intermittently misfire? Any other suggestions? I dont want to drop any money on coils if theres another option.

Maybe a petcock flow or gas cap venting issue?

Charging system working properly?

Voltage at coils?

How long since the last valve adjustment?

Fuel is flowing into the carbs just fine. Issue stipp happens if petcock is in prime setting. The bike is making about 14v when running and bat is new so i know its not a low viltage output.

I will check voltage on the coils ifni can find my volt meter.

And since i have had the bike (a little over a year)i havent touched the valves.

Do them. That's why bikes are sold. PO's are too cheap or too lazy to do them so they sell the bike saying the carbs need to be cleaned.
Steve

Andrew
The description in uour first paragraph is exactly whst happened to me when i had a kink in my fuel line (crappy clear plastic line). 10 minutes travel is about as far as i would get on a carb bowl of gas before the bike would cough snd splutter and die. Leave bike for 10 minutes while scratching head woul fill the bowls up again. A plugged or partial plugged gas cap vent would do the same. Perhaps check the fuel line for a kink that could restrict but not stop flow and try running with the gas cap open.

Valves are always worth checking.

There are tests in the manual for coils and pulse coils (the stock electronic ignition).

Other posibilities - loose connections at battery , fuse or somewhere in the ignition circuit.

Good luck

I will check the valves and coils if i have a chance this weekend. I know it's not fuel related. Fuel is getting into the carbs just fine. But ill check the fuel tank vent anyway.

I had a bike that did the same thing until I changed the fuel filter.

This bike has no fuel filter inline. But as i type this it occurs to me that it probably should haha.

I use these.
Steve