I came looking for a similar answer, and will continue to do so, but if the
gas cap is on too tight, this is what happens. ( I think gas caps are made
to vent, however, they don't always work that way)

Thought of that, just got back from trying a few other things.

Took gas cap off, same problem, but now it didn't even want to turn
over. Priming it will get it to start, but now it will just start, run
until the gas is gone from the prime and then stop. It is like it
isn't pulling any gas into the carb once it starts to run.