Gpz550 ignition issue

Got a weird problem on my hands that im trying to get to the bottom of. '81 gpz550 with a set of CR26 carbs on it, runs good, pretty peppy on the road, however i've noticed a couple times that it'll have a weird idle to it. Messing around the other day and i pulled off one of the spark plug boots on cylinder 4 and there was no noticeable change in the idle. Now, when i do the same thing to the other 3 cylinders the idle goes low and the bike stalls, naturally. Now the weird thing is that I've touched the cylinder 4 pipe and its the same temp as the other ones when idling, so it seems that it is firing? I've cleaned the pilot jet with no change. I've checked spark on cylinder 4 and even swapped plugs, coils, spark plugs, wires ect...no change. Is this a deeper issue like valves needing adjustment? 

Have you checked valve clearances and compression (sounds like one cylinder isn't working as hard as the others)

Thats what my next step is going to be when i get home later. Ill check compression first then continue on if that checks out, maybe even throw a new spark plug at it just for the hell of it. Might have to hold out and find some time to check the clearances though. 

Ant_5445 wrote:

Thats what my next step is going to be when i get home later. Ill check compression first then continue on if that checks out, maybe even throw a new spark plug at it just for the hell of it. Might have to hold out and find some time to check the clearances though. 

Tight valves will effect compression
Loose valves will mean reduced opening time so less flow "In" and "Out"

Ended up being a clogged pilot jet which was strange because that was the first thing i tried was taking the bowl off the carb when it was on the bike and squirting some carb cleaner through it...i guess i just needed to take the whole carb off and do a better job at cleaning. Then i was in such a hurry to make it somewhere with the bike that i forgot to re install the pilot jet! No wonder why it was still acting up on me afterwards and making me scratch my head haha!