If it only has 90 lbs of compression you might want to rebuild the top end. The kit runs around $150+.
If you want to get it running first you might want to start by putting a new plug in it and see if you can get her to fire.
I just bought a 1980 as well. It wouldn't start (fire) so I put a new plug in it and first made sure the plug was sparking by leaving it out of the block but plugged in the wire while turning the engine over. (had the rear end jack up in the air)
Once I saw it spark I put the plug back in and I put starter fluid in the carb and got about a second long run time off the fluid. So I knew the ignition was good.
Still wouldn't start without starter fluid so I moved on to the fuel system. I removed the gas line from the carb and put the hose end into a plastic bottle. I turned it over and got plenty of gas flow into the bottle. So it eliminated the fuel pump/tank/hose as the problem. So the only thing left was the carb. The carb was gummed up and quick strategic blast with the air hose and it freed the carb up enough to do its job and the engine fired up after that. Now I am in the process of doing a detailed clean job on the carb.
So the moral of my story is try and isolate your systems so you can see which one is failing. if you aren't getting a good fire from starter fluid then you may have problems with ignition. So a new plug would be a start. If that doesn't spark then let us know and someone can hopefully instruct further.
