Hi Rick;
   If you didn't take it apart and checked the ring, it make be stuck in the ring groove. Put it in a test stand, put at least a 12 inch prop on it, prime it through the exhaust, and see if it will run out the prime. A couple of those short bursts may clean out any gunk in the grooves. If the compression starts to feel better, then that is the problem, and may improve further with more running. Otherwise, it will just need a ring. To run it as is, see Randy Smith for a venturi and needle valve assembly. Randy's set ups use the "sprinkler" type set up, and it will be a bolt on process. Tom Lay used a different venturi position that requires a bit of machining for that, and I don't know who does that kind of work now that Tom and Byron Barker are gone. I have been in contact with Jim Lee about doing the needle valve location work for me on a couple of cases using a T&L engine as a sample, and I will let you know when I send mine to him if you are considering that. Frank Bowman is a source for rings and I need to contact him for what I need also. Randy can do all the work you need and you just need to contact him and send it to him. Your engine is an earlier version with no muffler lugs, and care needs to be taken when sourcing parts but will run nice when you get it fixed up. Nothing runs like a Tigre!
   Type at you later,
    Dan McEntee

   And now that I have my glasses on, I can see that it has muffler lugs! You still need to be careful with parts, as Tom Lay cautioned me about. Some versions were single ring, some double ring, and all parts don't interchange. I don't know about bore diameters either but Randy will and Frank bowman will. If you still have it apart, you can check ring gap and run that up the flag pole for a better opinion. Taking it apart and putting it back together will require the ring seating again, and it it's dry it will not make much compression. The burp test will tell a lot.
   Good luck and have fun,
    Dan McEntee

I'd be very tempted to just replace the ringed piston and liner set with one of Brian Gardner's (Bristunt) ABC assemblies.  The quality is excellent, and they should last indefinitely without any ring related problems.  A bit pricey, but worth every penny.

Andrew
It may come to that but I wanted to see what kind of shape it was in first.
Thanks
Rick