You're going to have to tell a bit more of the story if anyone is going to help you figure this out.
As in:
Describe how hard/not hard it is to get started at first and then how hard/not hard it is to get going after it has died. How well or how poorly does it perform when it is running? Does it give any warning before dieing?
Won't go into gear...ok...does that mean the lever is jammed and won't move? Or, does the lever move and it seems to be "very loose" as if it's disconnected down below? Or, it will move and it seems as if it MIGHT be shifting the transmission but the prop just doesn't turn.
I can tell you now that these props have a "shear pin" that can be broken and the prop will still turn but then, suddenly, not turn. AND, sometimes, the prop will catch again and turn if the pieces of the broken pin "catch" each other. These old motors came with a couple of spare shear pins mounted in a little holder under the hood so that you could get going again if one broke. Easy, cheap fix. Take your prop off and check that.
I would need more info to take a swing at the stalling problem. Hopefully the water pump is in good condition and it is not shutting off because it is getting too hot??? What is your opinion about that? These have a thermostat and if it sticks closed, it could overheat the engine but the water check stream coming out of the pee hole will still look ok.
Sounds like you just bought this motor and started using it but has it had any maintenance? If so, list what's been done. That will help with the diagnosis.
