With water ingress obvious - the carb tops have almost rusted through, the exhaust pipes have rotted out, and the engine is severely corroded, I wasn't expecting too much from the little twin. The inlet rubbers had come away from the alloy plates that mount to the head, which made it a little hard to get it running.
But today I decided to check the compression to get some idea on the internals, it wasn't pretty. 50psi was about as good as it got. That's why, in my opinion, it's better to get an engine running before strip down, but each to their own. Once it's running, it'll clear out a lot of the crap hanging round inside (and there was a lot of rubbish in the ports!). It puts pressure on the prison rings, which start to scrape the bores properly. Fuel/air mixture going through helps to clean valve stems and seats. All of this should help the low compression and, if it runs, gives you some idea on the bottom end. If you pull apart an engine without having heard it, you'll probably end up replacing every component inside for peace of mind.
