TOPIC:

Ive had my 1980 kz1300 20 k miles, a few years problem free. I started losing power ...maybe 30per cent .. after running engine fine for awhile...not overheating... then go to restart.. engine power reduced..still rideable... after hours or overnight starts and runs fine short or long distance until turned off and starting again. I feel like not enough gas getting to carburetors... doesnt have to be super hot. Shop said 3-4 cylinders werent firing.. I replaced coil still same problem.

any ideas if not the coil...or maybe nothing to do with spark...shop may be wrong.
thanks joe my first post here I thonk

If it is that 3-4 aren't firing I would be having a look at the pickups for that coil. Heat can effect those things and while it's running it may be getting kept cool enough to keep going but heat up a bit more once the real engine heat starts to get to it. Once they heat up and stop working they need to cool right off to work again. Just a gut instingt but worth a look.

When you say its losing power, is it bogging down when you crank the throttle or is it missing? Two cylinders not firing out of six will sound completely different then it normally does.

I dont think its missing.. because idle is still fairly normal..bogging down is good description...and suddenly it starts s working full power...this morning right from start up was bogging down but suddenly gained full power while riding in about a mile..

That is running lean check the carb rubbers for splits and air leaks even just the clamps being loose can do it. Also make sure the pistons in the carb slides are free and not binding and are returning freely to the bottom after you push them up. As you open the throttle the engine needs a richer mixture and it isn't getting it.

In disassembling another set of carbs I recently purchased I came across something that gives me reason to make a comment regarding your suspicion of fuel starvation. This is not a definitive answer but certainly gives cause for investigation.

First; The float-bowl for the left carb. had a significant amount of rust collected on the left side of the bowl. The center and right carb. bowls did not have this build-up. It would seem apparent that the tank on the former bike had significant rust issues (and no fuel filter) and given that the fuel "tee" is between the Left and Center carbs the build-up in the left bowl is logical. The debris would flow from the tank to the "tee" and given the bike spent time running on the side-stand, the heavy rust sediment would naturally flow down-hill from the "tee" to the left carb. and accumulate in the lower side of that bowl (when on the side-stand). Additionally I discovered a solid "plug" of similar rust debris completely blocking the fuel port immediately above the Float-needle valve-body of the Center carb. This blockage would have rendered this carb. completely incapable of receiving adequate, if any fuel. Having said this, it is possible that enough fuel could seep through the blockage giving enough fuel for idle but certainly not for anything above idle. Unfortunately I had removed this blockage prior to seeing this thread but the explanation should be self explanatory. The photo of the slides shows significant dirt on the inside which is testimony to the fact that the bike had been running with no air-filter or a damaged one. Operating any engine without a good quality air and fuel filter is inexcusable, defies logic and shows either the lack of comprehension for their requirement and/or speaks of someone's desperation in trying to solve an issue in a misguided manner.
Cleanliness, my brothers ! Cleanliness ! If your filters don't capture the crap; Your carbs will !