Help sorting out mech. fuel pump?

[cam.man67]

Decided to replace the fuel pump on Lester, we'll see if it gets him running again. Got fuel up to there, so it should. Here's the confusing part:

The pump I pulled off and the new one look identical...except that teh old one had a line close tot he inlet. Oddly it ran to the fuel filter. It doesn't look like the primary fuel inlet, so my question is what is the purpose that inlet/oulet/bypass/whatever? Do I need it? Is it a deal-break that the new pump doesn't have it? Does it have something to do with the fact that the orignial engine was a Olds diesel? The old pump part number is Carter 0-1955.

[cam.man67]

Ok, so I;ve been reading...looks like the mechanical fuel pump I took off had a return line and for whatever reason, that was the line the PO put the filter on. Now the question is...do I need that return line? Or can I cap it off and not worry about it?

[motornut]

the main is 3/8
vent is 5/16
the return is 1/4 and it helps with vapour lock
better to use the right one
but i've seen the two line used instead of three

[dwntwn]

X2 what Motornut said.
I've capped the return line and had no issues, other times had flooding and hot-start issues. Not worth the headache, just get the right one, you'll probably be happier in the long run