Do you have a another
fuel line and
fuel tank you could try? From the
fuel tank, all the way to the motor connection, reuse nothing.
At this point I would tear the carb down and throw it in my ultrasonic cleaner and blow all the ports out. Put it back together and run it again. Could be something intermittently getting into one of the jets, or something strange like the float getting stuck, in the up position (Never seen that before).
If it were me and I exhausted all other tests I could think of, I would replace the fuel pump. The issue is caused by fuel starvation, and there is not a lot on a motor that small to cause this issue.