RE:FUEL PUMPS 101:

[Stewart G Griffin]

1) What is the return line really for?

2) If, in a situation, where the carb only wants or needs say 4-5 lbs, but the pump puts out 5 1/2 to 7lbs., would having a return line help the situation assuming the carb float can hold back the 5 1/2 to 7lbs?

3) If, say, we switch to a more appropriate pump---one that puts out 3-5lbs AND HAS NO RETURN OUTLET ON IT, can we/should we plug the return line to the tank with no adverse side effects?

[Irish_Alley]

i think return lines are mainly for emissions probably wrong but that what it seams to me

[78 Chevyrado]

My 78 had heavy duty emissions on it.  Basically the only emissions device it has is the pcv valve and the heat riser valve.  It didn't come with any kind or return line.  It's not a problem for mechanical pumps.

[Cowman85]

i'm running a red holley electric (97gph, 7psi) with no return line and it seems to be running pretty rich, i do smell gas sometimes so i could imagine i would benefit from hooking mine back up...

[VileZambonie]

i'm running a red holley electric (97gph, 7psi) with no return line and it seems to be running pretty rich, i do smell gas sometimes so i could imagine i would benefit from hooking mine back up...

You should be running a fuel pressure regulator. Something like this

[Cowman85]

ya i've been looking for one but no one seems to carry them around here, i might have to order one off the net.

[HAULIN IT]

Stew, I'll try to help with your questions.
 1) A return line can have a couple purposes depending on the application. The one is to keep the pump cool, a constant flow of fuel can not heat up like fuel that is stagnant. Also, the pump will work easier/likely longer if it is not "dead heading"...try sticking you finger over a bicycle tire pump & pumping...it will be difficult, then go, this is what a fuel pump does at idle...up to the bypass & open, up tto the bypass & open.
 2) Yes, this is another reason for a return line. The vehicle needs X fuel pressure while making power, but at idle it needs very little. The second part of question # 2 isn't correct, "assuming the float can hold back the 5 1/2-7 psi", the needle will not see 5 1/2-7 if that's what the pump is making. If the return line is big & not restricted in some way...you won't have any fuel pressure. The return line bleeds it off, so to answer your question, yes it will "kill" the excess pressure if done correctly.
 3) For this reason, If you have a pump that only puts out 3-5 psi, then yes you would not want to use a return line, if you do...it would need to have a very small hole, just enough to accomplish #1, if that is your desires. If you have a lower pressure pump, the return can be plugged without problems, in fact, it may eliminate one. Lorne   
   

[Stewart G Griffin]

So, plugging the return line would not cause the fuel tank to colapse?   

[VileZambonie]

The fuel tank vent is what allows tank pressure to stabilize not the pump return.

http://www.secondchancegarage.com/public/535.cfm

[Stewart G Griffin]

Ok, cool.

[HAULIN IT]

No Stewart, that couldn't happen. Think of it this way...the return line was BRINGING fuel back at low pressure. Taking this away has no side effects. If in a worse case mythbuster mode & you made an extreme return line (shop air supply numbers - 130 psi, maybe) the tank would SWELL, not collapse. A vacuum is what would make it collapse, even the vent being plugged won't make it collapse...not run & hard to fill maybe. Lorne

[Stewart G Griffin]

Ok, cool again.

P.S.

In my (desperate)research, i came across this awesome online video course concerning fuel pumps and fuel systems.  i think you get a certificate and a hat if you pass the test.  Not that i care about that---i'm just saying.  i don't have time to watch it but here it is:

http://www.fueldst.com/FDSD/Player.html


2)What fuel pressure should a Rochester 2G be getting?