I’m no expert on them but I’d say your compression was stellar. Likely your problems are elsewhere; many of those motors had a waterpump in the lower unit that splashed water on the lower crank seal to keep it cool. (If not then it has a tube aft of the prop for the same job – not having the prop is like not having the water pump. And the prop tube won’t work really well {if at all} in a test tank even if the prop is on there.) If the water splash feature is not functioning, you’ll cook the lower seal and bearing and that may cause some of the problems you are experiencing. The impellers are not easy to find and are quite pricey – eBay may be your best source.

Yes, those carbs are TERRIBLE and that pump is very problematic. The only real luck I’ve ever seen with getting them to work correctly was when you could order the whole carb new…. I take it you’ve adjusted the needle valves and that hasn’t helped?

Lastly, starting in the 1970s many of the Eskas used a solid state ignition that was very trouble prone. I can’t recall if the 4.5 had it but if it is solid state then you need to connect with a man in Danbury CT that is the guru of them – here’s his website: http://home.earthlink.net/~edstoller/id16.html

You’ve spent a lot of time and effort on a motor that is not really popular and most would have dismissed. Your uncle should be VERY APPRECIATIVE of the work you have done!