Regulating pump bubbles
 

http://www.perrypumps.com/Pics/WEBPICS/pump.jpg
Sorry I have actually double posted this in other RCUniverse forums as well.

I have this VP-40SG Regulating pump.
The fuel line is ok from the tank to the pump.
But I see bubbles coming out after the pump, especially under full throttle.

I tried priming the pump, but I still see bubbles.
It is not very good as my engine fires inconsistently during full throttle.

I tried increasing the fuel flow rate of the pump (by turning in the screw).
But the bubbles remain.

Wonder if my regulatory pump is faulty?