1979 CB650 with bad compression

[adr3naline]

Hello everyone! I'm new to the forum here as I recently got a 1979 CB650. I had been on the sohc4 forum, but it looks like there is a LOT of great specific information here!

Anyway, I got this bike and have gone through and fixed a lot so far, but I couldn't get it to fire up, just crank. Tonight I tested compression, and after adjusting the valves, I've got in cyl #1 90psi, #2 30psi, #3 30psi, and #4 90psi. The service manual says it should be at 170psi.

So, since I know my valves are to spec, and I don't seem to have any leaking head gasket... I'm assuming I've got issues with my rings.

So, since there are so many experienced CB650 riders here... are there any known issues with these engines that may affect the compression?

Also, can I remove the head and cylinders with the engine still in the bike?

[Volker_P]

Welcome here!

Compression test is done with the throttle open. Hope you did it that way.
If still the same, try to give a tiny bit of oil into the cylinders. If it gets better, it's a pistons/ring issue, if not it is valves or some other leakage.
If these should really be the true values, your pistons/cylinders/rings will look like a mess!

Head and cylinders will come out with the engine in the frame. You'll need a small enough torque wrench and follow the stepwise pattern to avoid thread damage. I would recommend to clean out sand and small stones from the head bolts heads before you open anything.

BTW, ignition cables go from left coil to 1+4, from right coil to 2+3.

[adr3naline]

I'm excited to retest it, because I didn't have my throttles open. I also know that I've got to rebuild these carbs, which should help. I'll keep you updated.