You probably should see what the distributor says? Sounds like your cover is turned around or something wrong with the diaphragm? As far as pressurizing the tank, it shouldn't have much to do with the diaphragm? That's timed by the crank. Maybe you have a crankcase leak?

On the Cline duck bill check valves, they rarely ever work to begin with. The rubber is stuck together. you have to nudge them open the first time with a pencil or something.

Good luck,

Jim