Thats a great Shot, just what Ive been looking for! Thanks.

I see the little plungers, so one would open up while the other closes when you push down on the primer pump, and then the other would open and close when you release it, essentially a one way valve, allowing the fuel to pass only one way all the time. It appears because there is the extra resistance comming from the primer pump, vacuum preassure builds in the lines and wherever the weakest seal is it lets in the air. I wonder if perhaps the amount of resistance is whats really causing air to get into the lines because somethings got to give somewhere if enough preassure is built would it not? However if this resitance is normal then yes I definately have to keep working out the leaky lines.

Whats the big spring in the center for?