Mine has been doing something similar - seems to have started with the onset of cooler weather. When I start mine in the morning (no foot on pedal), it starts, but coughs and sputters for a few seconds....then it recovers and everything is fine afterwards...I was thinking this was low fuel pressure, perhaps as you indicated, losing it's prime.

I wonder if the fuel filter could be part of the problem...? although, if this was the case, I would expect the problems to be more prevelant.