Steve - having same problem with 'Mo i picked up off craigslist - seems to be a vaccuum issue on mine
I've had to open the gas cap a 1/4 turn, hit primer bulb 3x times, then choke, pull start w/care so gas doesn't pour out. Reseal cap and good to go.
I had replaced the fuel line, filter, and the fuel line gasket at the tank, which has a FAR tighter seal than my older 'Mo has. Just opening the micro-valve @ top of gas cap was not enough to release the vaccuum. At 2K' lower altitude, it starts right up w/o any other actions required
BTW, good to meet you a few weeks ago out @ the mile (that day we were out @ suckers cove and you came out later that morning)
hope this helps