Low compression, oil out the breather. kz900/1000

I've posted a little about this bike trying to identify what I have, incase you missed it here's the short version.

1980 KZ1000 G (z1 classic), fresh paint, new tires, super clean.
I bought it non running, heard it fire on ether.
It's has a frankenstein motor in it, 1976 kz900 bottom end, later model kz1000 cylinder block, a kz900 head (6mm studs) and unknown internals.

I put tires on it went through the carbs, points etc. and got it fired up and running well enough to test ride.
I did a post test ride rejet, coil relay mod and rode it about 40 miles today.

The bike idled and rode well, I could ride at highway speeds no problem, no smoke out of the exhaust, no strange noises. Once the engine was hot it would die at idle and be very hard to restart. There was also a steady stream of oil smoke coming out the breather tube that had been mounted high and rear under the seat. I put a makeshift catch can under the seat and collected about a tablespoon worth of oil in about 40 miles.

While the engine was still warm I did a compression test and the results were not good.
#1 cyl. 130 dry, 150 wet
#2 cyl. 95 dry, 150 wet
#3 cyl 55 dry, 90 wet
#4 cyl. 130 dry 150 wet

Best case in my novice head is rings, hone all around and valve work needed on 2 and 3. This repair would be a pretty big job for me but is kinda next in line on my vintage bike education. The scary part for a novice like me is that it's a complete unknown as far as the internals, guess I won't know until it's open.

Any advice before I tear into this thing? I just want to make sure I'm thinking about this correctly before I create a huge project.

Before you open up the engine perform a leak down test. That will help identify where compression is being lost. Keep in mind that while it may be the piston rings it also could be valves, etc. Once the cylinder head is off the chance to do a leak down test is lost. You should be able to borrow the test equipment for free through a loaner program at any major auto parts store such as Advance Auto, Auto Zone, etc. Those programs are great! Ed

Have you measured and adjusted the valve lash yet?
#1 thing to do "right now" if no.

This combined with the higer compression readings "wet" is what lead me to think rings instead of valves, although I've not checked valve adjustment.

I'll check on leakdown equipment tomorrow,

Valve adjustment first. If a engine is running bad, it will burn more oil and lose compression. Lean will make it overheat and do it too. Bad valve guide seals will let hot exhaust gasses into the engine and cause blow by.
Steve

Thanks for the advice folks, I'll be pulling the cam cover tonight after work if I have time and check the valve clearances.
At this point if the problem is confined to the head I'll feel a little better about it.

I'll post pics and results.

Thanks again!

As mentioned above, badly out of specification valve lash and dried out valve seals could cause these symptoms. Valve lash adjustment is too often ignored by ignorant riders because it seems too scary to do themselves and too expensive to pay somebody else, so they let it go until the bike is running too poorly to be fun. Valve guide seals get old and brittle, which allows them to leak. Replacing them is a bit more involve than adjusting valve lash, but it is perfectly doable.
A genuine Kawasaki factory service manual will be invaluable for either job, even on a Frankenbike.

Valve adjustment should be the first thing checked on an old bike like ours. I don't even bother trying to start an old bike unless the valves are adjusted first.

I've had 3 cb's, 2 gpz's and this is my 3rd Kz all in the past 6 months. I've been lucky and got them running by learning how to rebuild carbs, track down electrical issues, set ponts and timing etc.
I was due to get one that would require a bit more work, the things learned on the previous bikes gives me the confidence to tear into this one.

The bike is in great condition, it was priced well and I doubt I'll ever find a better keeper for the money I have to work with.
I'm sure I'll have tons of questions. The bike deserves to have the money spent and the work done. This is my first "big bike" and if it runs this well wounded I'll love it when its fixed.

My Factory service manual in the mail.

What diameter valve shims does the 900 head take?

MadShad wrote: What diameter valve shims does the 900 head take?

Z1 Enterprises sells shims and has information about size.

MadShad wrote: What diameter valve shims does the 900 head take?

29mm. jetsrus.com/valve/valve_shims.html
\Steve