I've got a 2-line pump on my BBC (3/8 supply, 1/4 return) and am cranking the engine temporarily from a bucket of gas. Gas tank not installed yet. Are both lines needed? It looks with 2-lines that the gas just returns to the bucket from the 1/4 line....

If its just temporary just plug the return line.

Dave

plug the small return line, and make sure that your fuel supply is up higher than the fuel pump to help gravity feed the inlet and keep it primed.

Besides plugging the return, that's a great idea to keep the gas above the fuel pump. Never thought of that but I bet that will help. Love this site; thanks.....

First Guess: If you look inside that 1/4" nipple, you'll find it's restricted down to a pinhole somewhere in the tube.

You shouldn't "have" to plug it; it should be nearly plugged all on it's own. You could just route it back to your fuel bucket with a length of hose. Plugging it will do no harm, though.

The point of that return is to bleed off fuel vapor, while passing a minimum of liquid fuel.

Schurkey - It might be possible (although rare I would think), that the new fuel pump is not working correctly. The return is also in the temp container and it sure does seem to return quite a bit of gas; more than just vapor; although it does bubble quite a bit when submersed....

What is the fuel pressure at the carb? That's what's important; and answers most of the other questions.

If you have adequate pressure at the carb at max RPM/WFO you're all set.

For the purposes of testing in the present situation, adequate pressure at the carb with the engine running should be enough to verify the pump.

If the fuel pump return is "bubbling"; and this is a cold-engine testing session--I'd be wondering where the air is coming from! Air leak into the suction side of the fuel system??? I suppose some bubbles at start-up are OK, but they ought to go away as the engine runs and the pump removes all the air from the fuel system.

sounds like a marine pump with the vent..

sounds like a marine pump with the vent..
If the small nipple is on the bottom of the pump; it's a vapor return. If it's on the top side; well away from the inlet/outlet fittings--you're right, might be marine. And there should be NO (zero, zilch, nada) gasoline coming out.