Low Compression?

[saaz]

It only takes a little squirt of oil...teaspoon or so. If the centre cylinder readings improve, then ring problem. If not much improvement, valves (they run hotter on the inside cylinders as well)

2&3 can often run lower as the inside cylinders get hotter on air cooled 4s. Your readings are quite a bit lower..I usually see only a 10psi drop on mine (both when it was standard at 80,000kms and when a big bore kit was fitted just after that..I currently have 145,000km on the bike)

Unless performance is down a fair bit, keep on riding. Before the rebuild, mine was at 100psi and using oil..smoky but still went ok!!

 

[Don Lobacz]

That 40# drop sounds like a fluke (sometimes the o-ring on the gauge adapter doesn't seal right). If you recheck it after running and consistently get these numbers, then I would agree with Saaz that it should be OK to run like that. A topend teardown is really not that hard, either, and that will let you decarbon the valves/combustion chamber, lap the valves, replace the valve seals, and inspect the bores.