1981 kz550 ltd engine bogs down

I had a very similar issue. Engine would run well for about 10 minutes of riding, then would begin to loose power and eventually stall. A clogged gas cap vent was the culprit. Vacuum would build up in the tank from fuel flowing out and air not being able to enter the tank. This would eventually stop fuel flow to the carbs and cause the engine to stall. I verified the problem by riding the bike with the gas cap cracked open. It would not stall with it open. After cleaning the guts of the cap, all is well. It's a long shot, but worth a try!

Those are TK22 manual-slide carbs. (Later 550's had TK26 CV carbs.)

As long as the carb float needles and seats are in good condition, the bike will run completely normal in prime position, as long as the petcock is not clogged up and restricting flow.

It sounds to me like the petcock or a fuel filter is restricting flow. (Prime uses the reserve pickup tube, just FYI.)

If you are using a see-through car fuel filter with a pleated paper element inside, that can be the problem. They require fuel pump pressure to allow flow. Gravity is not quite enough with them, and they gradually stop flowing, even when new.

It could also be the gas cap issue as JaFlo mentioned.

Again, thank you everybody for the help.

I've ruled out the gas cap possibility. It still dies when the gas cap is open. Also, the fuel flows freely with the petcock in PRI. The fuel filter I have is new, and is the metal type. I basically replaced what was already on there. Honestly, it is probably a carb issue and I need to rebuild them, but I'm going step by step and learning as I go. The inside of the tank has a little rust too, so I"ll have to clean that out.

Looking online, I found various diagrams showing where the vacuum line connects to the carbs, and where the floatbowl vents tubes have to be pointed up and open. None of them helped me figure out exactly where they should connect to my carbs, though (vacuum line and floatbowl vent tubes). I took some pictures, maybe someone could point out for me whats happening here? I've also marked them up.

'A' are all sealed, except for on carb #4 ('D') which has that little bit of a line on it.
'B' doesn't seem to be answer.
'C' comes from the rubber hoods on carbs #1 and #4, and just connects both of them (going nowhere).

Any help? I will know these carbs inside and out by the time I'm done with this.

Also, the float bowl overflows are all capped off with rubber nipples. I think they were leaking or something. Is that OK? It seems like they should be open. I will be rebuilding this sucker but I want to see what happens when I have all the tubes on correctly first, and I can't find enough details online.

Those nipples that are on the engine side rubbers are for syncing the carbs and 1 4 should not be joined they should be plugged off with a rubber cap.

The bowls should have a drain lines that routes down the right side of the bike near the clutch cover and should not be capped as the bowls have a drain tube to stop overflow into the engine.

From the picture B are your idle mixture scews it adjusts the air,

A is just sealed off casting

You could use the pipe that is connecting 1 & 4 for the vacuum petcock then just cap off 1 & 4 as it should be.

Thank you razmo99, but I still don't understand exactly where on the carbs the vacuum petcock line is supposed to connect to.

vac petcock connects to the #4 carb. There is a pipe coming out of the carb. The other 3 carbs do not have that pipe.

Thank you that's what i was wondering

I had the same model as yours for a couple pf years,when I got it I put pods on it and never re-jetted it,read somewhere on an engine that size and smaller it doesn't need it for pods and it ran fine.So your problem can be too large main jets and your flooding the engine.If your rebuilding it,look for stock size main jets on Ebay. The overflow tubes inside the float bowls have a tendency to break at the base,this could be the reason for the rubber caps.Check the plug wires,they go 4-1 left to right if your sitting on the bike.When I bought mine it would run,but no power then die until I figured that out.Check your timing mechanism,it needs to have a drop or two of oil once in awhile.Like you have planned already,clean the primary contacts on the coils,make sure the spade connectors are clean and tight,not sure about the plug wire go to a local bike shop and buy new wires, they just screw in to the coil and caps,for a few dollars,won't hurt.If you haven't gotten it yet,go online and download the service manual,I got mine for free. think that's most of the problems I had with it,most of te rest was PO caused.Likied that bike,was fun just to run around on.

The 550 C model needs to be rejetted for pods, but only slightly. You can get away with actual stock jets, but you will need to shim the needle. This will need the slide to be shimmed accordingly with a shim wire (guitar strings work perfectly for this). Without the rejet, you will have cold running headaches and even warmed up, it won't be happy.

Thanks for the advice everybody. I have all the tubes/caps connected in the right places now, and the vacuum line seems to be working (albeit with a very slight leak). One of the carbs leaks alot of gas out of the drain/overflow screw on the bottom of the bowl when I run it, which is why the PO capped it. AKA it seems like he had no idea what he was doing.

My next task is to disassemble the carbs and put them back together correctly, and to replace the shifter bolt, where the seal where it enters the transmission is leaking oil. I won't be able to get to them for a few days though. I'll keep on updating.

Lou is bang on about the rejetting requirement for the 550-C ran mine with pods for a few days when I first got it running (was soaking the air box boots so they would soften up) it ran good was no where near perfect

I think I adjusted the pilot screw on mine,it ran good,maybe would have ran a little better if I jetted it.The plugs looked goos when I pulled them,so I left the carbs alone.Did you spray the carb boots with stater fluid or WD-40? If not spray them and listen for a change in the rpms.When you pull the carbs,look inside the float bowls,there's a brass tube that breaks,I used Goop's Seal -all,it's gas and iol resistant.It lasted a couple of years,of course best thing to do is replace the bowls.