ORIGINAL: pe reivers
There seems nothing wrong with either prop or fuel. The problem is in the carb, (maybe water drops in the fuel)
If there is debris floating inside the carb before your needles, that explains the behavior you are getting. Good one minute, crappy the next.
Give the carb a good rinse, and blow out fuel passages. Repeat a couple of times. If you have access to an ultrasonic cleaner, use it with a gasoline bath and a syringe to pull fuel through the needle jet passages while still under sonic waves. When done, enjoy the debris inside the cleaner tank and go fly.
The weird thing is that once we get the engine running, it always seems to run well from that point onward for the rest of the day, until the next time I bring the plane out to the field, that is.