Domenic, if your pump is pumping it must be sucking! My mechanical pump has had no trouble priming my system ever. When changing filters I drain the lines once replaced a few strokes on the bail and fuel is in the bowl
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All pumps suck or they would not displace the volume to push it as you say.
How much the pump is capable of drawing fuel (sucking) is contingent on the condition of the check valves and the volume being displaced. Most pumps have a rating as to how high they will draw or the "suck rating" rated in inches or feet. Some will actually state the amount of draw as a vacuum value which is the draw or "suck" value. Once the pump is primed the pump will draw what it displaces.
The air in the system will be vented by the vent in the carb as the air gets to the carb. there may be a few air pockets left but there most always will be. You can see it in the clear type polishing filters and it has no affect on performance. With fuel injection you need to get the bubbles and air pocket to a minimum for consistant fuel preassure at the injectors.
Dave Neptune
