YZF750 compression results. help needed.

[twack]

My YZF750 runs like CRAP so i did a compression test and i got back 90 30 30 90. so time to dive in. but what usually causes that kinda compression in these bike? Rings? headgasket? valves? Any help would be awesome.

[yamaha_george]

hi,
Most likely the top gasket in this case since it is the 2 middle cylinders that are VERY low.
Whilst looking at that I would take the opportunity to set the valve shims to the correct specs. and check the two center bores for damage (just a pre-caution )