raron455,
No possitive pressure is needed. The carb has in internal fuel pump.
I would look into the air bubles in the fuel line .It could be nothing but it would be wise to check all lines and fittings including inside the tank.
I ran amzoil Saber at 100:1 in my engines for years with no problems . I have changed to Stihl Ultra but only because of avail. and pricing not because of any issues with Amzoil. The secret is proper tuning and cooling . I see no issue with using it at 80:1 as Brison recommended . Let the oil wars begin.

BTW , If I ever get to travel to Waco I may take you up on your offer.