I fitted a two stroke carb to a Honda 31cc four stroke once. I used a small spring in the fuel pump, and plumbed the pump pulse to the intake tract. I too was worried that the pulse would be insufficient when the throttle was wide open, but it worked. Pumped plenty....

Stihl's answer to the problem on their Four Mix four stroke design was to use crankcase pressure, but with a booster chamber with an extra spring loaded diaphragm in it on the carb to help the fuel pump. They also used a large diameter hose on the pulse line.

AV8TOR