Yep... something is up with the gauge or the way you tested. 50 psi would not run.
Check to see if the O-ring is around the part that screws into the sparkplug hole. Also, check for any other leaks.
When you do the test... you need to hold the throttle open, and you need enough power in the battery to crank the engine at a good, normal starting speed.
If you are having a hard, warm re-starting problem... either your needle and seat are leaking... or your carb diaphragm is stiff. (or not OEM Mikuni) Either of those issues will allow the fuel to leak out of the carbs, and into the engine. This is a 2 fold problem. First... the engine is now lightly flooded, and second... there is no fuel/pressure in the pump side, so now, it has to crank to get fuel into the carbs.
If this is the case... when you find yourself with this problem, hold the throttle open, and then crank. It should catch, and run, but it's best to fix the problem.