life = what kz550

finally got bike on working on my kz after a like 6 month break (got a ninja 900r so i worked on that instead) and i finally got around to fixing the electrical issues fuse blowing etc, i just checked the comp. on all 4 cyl, heres the order

1. 150 2. 150 3. 135 5. 150

Cyl #3 has something wrong with it, can't figure out what on top of my head really, valves or rings i'm figuring but is there a way to figure out which one it is without taking it all apart?

my actual problem though, is it starts and runs, but only on cyl 2 and 4, they all do spark but the spark seems weak on all 4, i don't know if it's because of the small plugs (first time using that size plug) but they seem weak and all 4 are new. Carbs i got rebuilt so those should be good, i'm going to check the voltage on the coils when i get my tester back.

anyhow, for my cyl #3, comp is low but on top of your heads which would it be first? rings or valves? and it should run on 3 even with a lower comp then others right? just looking for opinions thanks

Generally speaking if all numbers are within 10% of each other youre good to go, you can check valve clearances and be sure (loudvhx has a link to a manual and valve train warning, check it out!) but if all is in spec you are good to go, make sure you have battery voltage to the coils and after that if only running on 2 and 4 your carbs are suspect, probably plugged idle circuits, gas tank nice and clean?

I would not yet worry about #3. I've seen one cyl @90psi that free'd up after a bit of running. I would, however, check valve clearances and make sure no one is too tight.

a good way to check valve,cylinder health is,do your normal compression test and record all the numbers,then, pull the plugs,squirt a bit of oil into each cylinder and test the compression again. record the numbers again.If theres not much difference twixt the numbers in the 2 tests then itll be your valves.if there is a big difference then its a ring problem. Remember to keep the throttle full open on both tests,dont ask me why though ,Im not a mechanic.
Good luck.

If one cylinder isn't running right the rings can loose their seal. Made right again and run the compression should come back up. If you have weak spark, then there is a electrical problem. Say if #1 is fouled than #4 can misfire but #3? What do you mean by smaller plugs? Sometimes when a motor is burning oil, you can put in a BP 8 ES rather than a B 8 ES. Longer reach. That's to burn the oil and prevent fouling but not a good idea. A last resort. I'd start with the stock plugs. There is a difference in heat ranges among the different makes whether they say so or not. The old Honda's came out with ND's but the NGK's were better at the time so everyone used them. That's a whole different story.
Steve

The carb is open during compression testing so that air can be sucked into the cylinder, which provides something inside the cylinder to be compressed.

If carb is closed during compression testing, content of the cylinder continues being pushed out through the exhaust, but very little air is being sucked into the cylinder to be compressed.

In other words, if there's nothing inside the cylinder, and nothing being sucked into the cylinder, there's nothing inside there to compress.

And of course a compression test may be satisfactorily performed without the carbs being attached to the engine.

Good Fortune!

I will try the oil test, thanks! And by smaller plugs I meant like, a car spark plug is fatter an that plug is thin, english is not my main language i am sorry for improper terms. I think I will take some coils off of my gpz that runs good and try them on the KZ see if the coil is going and not producing enough power. The gas is coming from a plastic tank (no good tank for it yet so i put my YZ250f tank for now just to try to start it. Thanks again my friends

Start with the stock plug.
Steve