KZ900 Engine Compression Concerns?

Just registered and first post so hope you can help.
Trying to get a 76 KZ900B LTD back on road. Got from brother in law who passed and I don't know the history except it was his bike and he was prior Kaw dealer. Should be good but has sat at least 10 years inside storage. Cosmetically very good and put some small amount of penetrating oil and minor amount of 20-50W in each cylinder and turns over fine. Has less than 13M miles and engine seems stock but getting a range of 85 to 115 PSIG compression test whith open throttle. A can see a lot of carbon on piston tops with plugs out. Also getting 11.5V at the coils which seems pretty good as have read a lot about problems with old wiring needing a new rely and wire to coils. Does this compression and voltage seem a concern? Do you see any issues with now changing oil and trying to start or do you recommend pulling value cover doing shims or even head, or something else before this step ?

The piston rings are probably stuck limiting compression. Yamaha makes a product "Ring Free" that's supposed to free up stuck piston rings.It might be found at Yamaha boat dealers.

Sometime just running the engine for 100 miles will free up the rings.


Mopar makes a combustion cleaner designed to remove carbon build up: Mopar Combustion Chamber Cleaner # 04318001.

It can break the rings if ran when stuck. I'd give the ring free a chance first and run it on the center stand a little at a time then adding ring free after. You could put some air into the cylinder when valve are close and listen at the carbs and exhaust for the air escaping. That will give you a heads up.

It probably won't take more than a good carb cleaning, a fresh set of B8ES, clean the points and set timing to fire it up. The ring free product would be fine to use.

Get it running. Put some miles on it and see how it goes. It's likely the valve seals are going to need replacing in the near future anyway. That's the time to address and piston ring problems you may have.

If it's still got the stock pipes and airbox, leave them on it....

Larry C

I might pull the vavle cover and check valve clearances for peace of mind. It will give you a good look at the cams, timing chain, and the top rollers on the chain at least. That way you can get a good idea of the general condition of the internals all for the cost of a valve cover gasket. 85 - 115 is low but as others have said, stuck rings, or valves that aren't closing fully due to improper adjustment could be lowering your compression. I'm sure that you could get it to start with that compression though.

Definantly change the oil, ring free, fresh plugs, clean points, probably clean carbs, and make sure that it has a new, clear, inline fuel filter so that any junk in your fuel tank doesn't clog up the carbs.

Thanks guys for all the good suggestions . I have already put a set of kz1000's M26's on that had been cleaned / checked out so feel this is covered. I will try the ring free after changing oil and checking points. Assume this is a additive to gas or spray with instructions but let me know if something additional on how to use is needed. Knowing that it likely will start at this compression I'll give it a try and see what happens and let you know. Probably will wait and see on the value cover after this step testarossa.
Another question if you don't mind. I am trying to install a rebuild kit in the front master cylinder as well but can't seem to see how to remove old piston parts. I have Hayes manual and know that it has a snap ring but can't even get beyond the dust cover which seems to have a piston stop in a grove but no way to remove. Is there some trick or tool needed here other than snap ring pliers if I can get that far???

I believe www.z1enterprises.com sells a long nosed snap ring pliers for just that same reason. I'd contact them and ask as they seem to know all about these older bikes.

2KZLTDs wrote:

I will try the ring free after changing oil and checking points. Assume this is a additive to gas or spray with instructions but let me know if something additional on how to use is needed.

I think you spray it in the spark plug hole and let it run down onto the rings.

If not done, you need to remove the gas tank and rinse it clean. Also, clean the petcock assembly.

you will most likely need to get the tank sealed to keep the rust from constantly pluging up filters and jets.

there is also a product called Sea foam, that can be added to the oil and gas to free the rings and clean the carb and carbon.

2KZLTDs wrote:

Thanks guys for all the good suggestions . I have already put a set of kz1000's M26's on that had been cleaned / checked out so feel this is covered. I will try the ring free after changing oil and checking points. Assume this is a additive to gas or spray with instructions but let me know if something additional on how to use is needed. Knowing that it likely will start at this compression I'll give it a try and see what happens and let you know. Probably will wait and see on the value cover after this step testarossa.
Another question if you don't mind. I am trying to install a rebuild kit in the front master cylinder as well but can't seem to see how to remove old piston parts. I have Hayes manual and know that it has a snap ring but can't even get beyond the dust cover which seems to have a piston stop in a grove but no way to remove. Is there some trick or tool needed here other than snap ring pliers if I can get that far???

I used the master cylinder rebuild kit on my 900. I have a picture somewhere of the pieces apart so I could remember how to put them back together. I'll try to post it this evening.

Thanks again guys for the additional posts. I did clean the tank electrically which worked pretty well not needed to be sealed. I also put two overly large gas filters on initially figuring I would change later to something more asthetic when I got the worst loose flakes out. Have heard of sea foam as well and maybe that is a better option than ring free but can try both as I think sea foam goes in the gas for the first couple of tanks where ring free goes in the cyclinders.
I will check further with Z1 on the brake cylinder rebuild as I need someting to get the first piston stop out before I even get to the snap ring stage that they sell a tool for. Thanks again for all the help here.
Last question is do you guys know any good KZ900,1100,1300 mechanics in the mid Michigan area who are skilled in these old bikes and interested like you are? I now have four of these and could probably use some local help especially on the KZ1300 which I would like to tackle next????

Here's the pic of the pieces disassembled. I do remember the piston retainer being a pain, but I think I was able to pry it out with a very small screwdriver or something similar...it's been a while.

Sorry about the quality - it's a cell phone pic.