The 86 FA50 I got going for my kids only shows 80PSI when I check it with my AUTOMOTIVE SCREW IN type compression gauge.
I also checked a Honda Elite, lawn mower etc, None of them read over 100. When I checked my truck it has 180. My FA50 runs great, starts on the 1st kick, plenty of power for my 120lb kid so my guess is compression gauges must differ somewhat.
Try taking the muffler off and try to start it. If the muffler is restricted it can't suck in hard enough on the intake side.
Also you could have a timing issue .
Keep at it, just remember to walk away when you get upset and come back with a clear head. I know from personal experience this helps a lot!!!!!