Tricky problem

Hey all I have brought this up before . I had an oil on sparkplug issue but I think i solved that when I had all valve seals changed and things cleaned extremely clean and new shims added. So I dont really have a sparkplug problem anymore but I still have 90 compression in both cylinders . The cylinder walls were very clean when I had the head off . Going to replace thehead gasket when I get a chance but I am still thinking piston rings are worn . This is on my kz750 twin btw . On another note I cannot get past 70 mph in top gear . Thanks trying to get this bad boy on he road with all the new add ons.

What are spark plug readings incident to high speed throttle chop test?

Would assure timing advancer is properly functioning and isn't stuck in idle position. Would view operation of the advancer under a timing light to hopefully watch watch it rapidly move back and forth as rpm is varied by blipping the throttle.

Could also do a leak down test to help determine source of compression loss.

If needed, here's some info about leak down testing --

A leak down test injects air pressure through the spark plug hole to pressurize the combustion chamber.

Can perform a poor man's leak down test by introducing compressed air into a spark plug hole and listening to where it escapes from the combustion clamber. This may be done at TDC or any other cam positions where both valves are fully closed. Top dead center (TDC) is when the piston is at its highest position. An easy way to tell TDC is by alignment of the T mark with the case mark when viewed through the timing window.

May introduce a spurt of compressed air by using a rubber cone-tip blow gun (rubber air nozzle) held into the spark plug hole. And of course keep holding it in position to keep air from coming back out the spark plug hole while listening for escaping air at other places. The air compressor should not be running while listening because the noise will likely drown out any sound of escaping air.

Air heard escaping from exhaust port indicates exhaust valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from carb intake indicates intake valve not fully closing (perhaps too tight clearance or damaged valve or valve seat).

Air heard escaping from crankcase breather indicates loss of compression past rings into crankcase (perhaps worn piston rings or cylinders).

Air heard escaping from head gasket area indicates indicates loss of compression past head gasket (perhaps due to a blown head gasket).

A leaking valve may sometimes be resolved by adjusting the clearance to within specs.

A leaking head gasket may sometimes be resolved by torquing the head fasteners when the engine is stone cold (such as after sitting overnight).

Good Fortune!

This reminds me of the previous thread about a 79 750 twin with oily spark plugs where I pointed out it was a complete waste of time to replace seals without doing the valves as well. My 79 750 twin went 75k miles before the rings wore out and they still held 125 PSI against decent valves (150 psi is stock maximum).

If you have 90 psi, I can almost guarantee your valves are not sealing.

My advice from the previous thread is still the same:

kzrider.com/forum/2-engine/590928-kz750-...-pistonsrings#604892

When the compression test was done, did you have a warm engine, throttle held wide open, and either a fully charged battery or a good solid set of 10+ kicks? If you add a bit of oil to the cylinders, does it come up?
Leak down test, like Patton posted is the best way to diagnose it. You would be best to use gauges purpose built, but the poor man method will show where the big leak is. You can add oil then also, to see how it changes. Since you did the stem seals, you must have set the valve clearances? Buy those odd size 750 twin shims, from where z1enterprises?

So I started the bike today and heard some air coming out. Plain as day I had slight oil on the rear left corner of the head gasket seeping out. Not a lot, but enough to run down the side after a couple minutes. I don't believe this is my cause due to it not leaking until after I reinstalled the head. So that needs replacing. Will try the air and leak test tomorrow to see what else it could be otherwise its my head gasket. And Motor Head I bought my shims from a local motorcycle shop for 5 bucks a piece. I have plenty of shims for my valves.

I just read on some random site that low compression in adjacent cylinders is a bad head gasket or rings . It might of been this gasket the whole time . Thanks

Is there anything I can put on the head gasket to ensure a good seal ?

A new gasket of good quality should not need anything to seal, assuming the surfaces are clean and not warped.

I am not sure I am reading this right, did you re-use your head gasket after you replaced the valve seals?

yes, And I this lesson is learned . Got a new head gasket on the way . I rechecked my valves and everything is in spec and sealed good. Popped the head off and i have quit a bit of oil in both cylinders . I am asuming my head gasket didnt seal right and let oil from passages into my cylinders . The cylinder walls are in great shape, I dont see any wear at all. I think it safe to say a new head gasket and some carburetor work will fix things. Any other suggestions greatly appreciated, cant ever know enough