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fuel pump return line???

R

RalleyRed

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I need some help guy's

I posted this on the wrong form before!

I just put a crate motor in my 68, Bought a Holley fuel pump for it.

Just noticed that while my car had a return line, the pump does'nt.

What I need to know is Do I need to replace this with a pump that has a return line or not.

If you could also tell me why . I'm very curious as to why some cars have a return line and other don't.

Thanks to all.

Rick
 

motorman

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Messages
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2008 Crystal Red Tint Coat
the return line was to relieve the pressure between the pump and the carb when you shut off the engine. you may have some flooding problems without the return line.
 
R

RalleyRed

Guest
Thanks Motorman


Could you tell me why some cars don't have a return line?
 

motorman

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849
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2008 Crystal Red Tint Coat
i think it has to do with the underhood emissions.
 

ChuckG

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63FI, 69BB
Original Rochester carb equipped cars used the return line (4 barrel cars) while Holley carb equipped cars ( 3x2 barrel) did not use the return line. Chuck
 

motorman

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Messages
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chuck the 3X2 are the ones that need the pressure relief because those 3X2 leaked thru and filled lots of 427 engine oil pans with gasoline and caused engine failure. back then a aftermarket co. came out with a little bypass to install between the inlet and outlet of the fuel pump to prevent this. the leaking of the carbs is one reason there were so many 427 that had their blocks changed. drilling a 1/8" hole in the gas cap also helped because the heat from the mufflers caused pressure to build up in the gas tank adding to the problem. even on the older corvette with the take apart fuel pump we drilled a .015 dia hole between the suction and pressure chambers to relieve the pressure on the carb after you shut of the engine.
 
M

mgms_1968

Guest
Ralley Red

The return line is also a way to maintain good pressure at the carb. The fuel pump will pressurize the fuel line toa specific psi 5-6 is what you want. Well if you do not have a return line and you are at idle you might have more pressure then you need and the reverse at full throtle.

Also another reason for a return line is that you have cooler fuel traveling to the carb, since some of the fuel is retruned to the fuel tank.

I had a document that talked about fuel pumps and the reason for return line. I will see if I can find it and post it here.

AC Delco makes a fuel fileter with a return line on it, I can not remeber the part number but it was the filter used on the 1968 427 vette with a 6-pack (3 2-Barrel carbs).
 
R

RalleyRed

Guest
Thanks to all,

I will read that thread mgms_1968, I ended up taking the fuel pump off the motor I took out so I should be okay for a while.

Thanks for the help guys.

Rick
 

motorman

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Messages
849
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Corvette
2008 Crystal Red Tint Coat
return line

mgms 1968, the return line heats up the fuel because of the pump action and the engine compartment heat and you keep recirculating the hot fuel. this was a problem on the 97 and 98 C5s so in 99 they removed the line from the engine compartment and do the recirulating in the fuel tank.
 
R

redmist

Guest
I installed a electric fuel pump, used SS braided fuel lines, ran them against the firewall to the center of the firewall and then straight to the 750 Holley. I wrapped the lines in heat insulating material as well.
No return line. No problem.
 
S

SwaveDave

Guest
Ralley Red,

When i went with a Holley Electric Fuel Pump on my 1970, i installed it at the rear bumper close to the fuel tank outlet. I installed a 3 way Mallory Regulator right after the pump ; one port is fuel from the pump, the other is fuel to the carb, and the other is fuel bypass right back into the top of the gas tank. Therefore, i abandoned the entire return line . I have my regulator set to put out 10 psi ... which gives me 7 psi at the carb.

If you ever go to an electric fuel pump, this info might come in handy. I had too many problems with mechanical fuel pumps and since i did a major increase in hp/tq on the engine..i wanted to be sure it was fed well.

Dave
 

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