For those still checking this thread:

I had all the same troubles you describe here. I just replaced a broken Reed Valve Cage and put in new Reeds. When I was putting it back together, I noticed there is no gasket between the motor and the phenolic block that the carb mounts on. There is a passage thru that interface that I believe puts the vacuum pulse on the fuel pump diaphram.

Well, I looked at it closely, and it sure doesn't look like it seals very well. Not only might you be loosing some of the vacuum to the pump, but you may also be pulling a leak into the intake. I sealed mine with a very thin painting of Pematex Silicone Gasket Sealer for good measure.

I'll tell you this... After all the troubles I have had flipping my ***** off trying to start this thing, and having to constantly resort to priming, my troubles are gone! I put it all back together, flipped it 10-12 times (it was all totally dry after disassembly) to get fuel pulled up, turned on the ignition, varroom! Choke off, second flip it started.

After that, I started it 14-15 times adjusting the needles. Started every time within two flips without choking. I am now convinced that I was either leaking air into the intake at the block, or not making enough vacuum to the pump, or probably both. It is sweet now. Cold starts, 2-3 flips with the choke on, blappppp... choke off, starts withing 2 flips every time!.