Did you check the things I posted before?
(The fuel line where it goes into the motor, that connector has a rubber seal that goes bad and allows the motor to suck air and die.
Another problem might be the float in the carb isn't set right and runs itself out of fuel.
When pumping the ball, does it get hard? No/ the fuel pump might have a bad diaphragm, check it.)
You said it started, just won't keep running?
Compression? The fuel pump won't work right if the compression is off.
The ball, has a check valve, if it's bad it won't work right.