CB77 doesn't run well, bad compression?

[mvdb]

I bought my CB77 a couple years ago, but I haven't had so much time to fix her up.
I got 1 new coil, a condenser and a fresh set of points so I have good sparks now. I adjusted the valves, got the carbs cleaned in an ultrasonic bath and flattened the flanges.
Though she doesn't wanna run fine yet. I got myself a compression tester, plugged it in and kicked the bike over a couple of times. Here's the results.

Left, about 116 PSI


Right, about 87 PSI


Will this be the reason for running poorly?
I'm not really sure what to do next. Spray soapy water and see if the headgasket leaks? Bad valves?

Thanks in advance

[cadman]

First did you do this with the carbs wide open? If not do it again.

Pour an ounce of Marvel Mystery oil in each cylinder and let it set for a day or two and recheck.

[mvdb]

First did you do this with the carbs wide open? If not do it again.

Pour an ounce of Marvel Mystery oil in each cylinder and let it set for a day or two and recheck.

Thanks for the quick reply.
Yep, throttle WFO! Not sure about the choke position though.
I'm not sure if we have that oil in Europe. Is that for checking the piston rings or something?
It will take a while for me to check this, not sure when I'm home again.

[cadman]

Throttle wide open choke off.

Marvel Mystery oil or .... something to loosen up the rings. They may be stuck in their groves and causing problems. We also have PB Blaster which is used for loosening rusted bolts - or you might even try WD-40. Let it set for a day or two and then crank with plugs removed to clear and recheck compression. This is essentially a somewhat dry test.

Next would be to put a tablespoon of oil in each cylinder and see what happens. If the compression goes up dramatically probably poor ring sealing - if it goes up marginally then probably valves.

[jensey]

Hi,

where are you located ?

Jensen

[cadman]

Marble Falls, Texas

[mvdb]

Hi,

where are you located ?

Jensen

In the Netherlands just like you!