7t2vette

My 72 has a return line from pump to tank. I will be using a holley mech. fuel pump that has no provision for a return line. Can I just block it off and not worry about it?

clem zahrobsky

yes, but you can not do this if you use a pump made for the return line as you will have excess pressure. :chevy

7t2vette

The Holley pump I will be using has no provision for a return line, like the stock pump has, so do you think it will work? What was the factory's reason for having the return line anyway? Will this cause any problems in the future?

clem zahrobsky

to relieve the pressure to the carb when the engine is off to prevent emission problem. having the pressure cut off to the carb when the engine is not running also could prevent carb flooding. :chevy

PRNDL

I have been asking this question for a long time of a lot of people and I have gotten a few different answers. First of all, we know that in 68 and 69 the fuel return line came off the fuel filter and was only used with Rochester Qjet carburetors. So whatever the reason for the fuel return line, it was needed for Qjets but was not needed for Holleys. After 69 the fuel return line came from the fuel pump, but still (I think.....) was not used with Holleys. So (again, correct me if i am wrong) the LT1 cars for 70 - 72 did not have fuel return lines. All other cars had a Qjet and a fuel return line that comes off the fuel pump.

So, what is it about Qjets that require a fuel return line but Holleys do not?
I have most frequently been told that -

1. At idle, the stock mechanical fuel pump supplies more fuel pressure than is needed by the Qjet (not sure why a Holley can handle it), so without the fuel return line you will get too much fuel in the carb - at idle only.

2. I have also been told the fuel return line cools the fuel and prevents vapor lock. Again, not sure why you wouldnt have the same problem with a Holley carb.

My personal experience is my 68 L36 had the fuel return line blocked off when I got it. I have not experienced any problems at idle. I have had some problems that might have been vapor lock. This occured only in hot weather and only under full out acceleration.

I still would like to hear from someone... maybe someone involved in the actual engineering of these cars to tell me why the Holley equipped cars did not need the fuel return line that was used with Qjets.

There are lots of cars running with the fuel line blocked off. Doesnt make it right, not recommended, but doesnt seem to create any serious problems. MJ


[Modified by MNJack, 1:34 PM 11/3/2002]

clem zahrobsky

the holley has a lot more fuel bowl volume because of the 2 float bowls. with the fuel trapped between the fuel pump and the carb expanding it causes the Qjet to spill gas into the engine and cause emission problem. with the return line there is no pressure buildup between the fuel pump and the carb so the Qjet does not bleed fuel. fuel pumps with a build in return line have a lot more pressure if you block off the return line causing the carb to flood. a good trick if your fuel pump goes south out on the road just block off the return line and it will get you home. if you block off the return line on a good pump the pressure will go to over 9#. i had to install a fuel pressure regulator,"been there done that" on my pickup when i added a extra fuel tank and had to remove the fuel pump to tank return line to prevent excess fuel being pumped into the full tank causing it to over flow. like i said "been there done that" :chevy


[Modified by clem zahrobsky, 5:26 PM 11/3/2002]

73 LS-4

I did this swap last year, and was kinda concerned about having the return line capped and what problems it might cause. I heard that vapor lock was the biggest concern with this swap, but I haven't run into any sort of problem with this, and mines a big block with headers so its a pretty bad case scenario. So I think you'll be just fine.

:cheers:
Pat Kunz

Gordonm

The LT1 cars had no return line and a 3/8 fuel line. I have blocked off many return lines on other cars and never had a problem.

jdunne

I have a holley blue with holley 750 vac/sec now.....when i first installed the pump it was with an external regulator and no ret line with an Edel 750 vac sec.....i round that the Edel was extraorinarily sensitive to fuel pressure,any more than 6(even as a transient) and it flooded.....then swapped to the holley and found that not so sensitive to fuel pressure,but when i installed the return line it seemed to quieten down the pump and stop some minor aeration in the line that was causing some noise......it still isn't quiet,but at least it has lost the occasional sound like a turbine spooling up...john :chevy ;)

7t2vette

Thanks for all your replies, I am still undecided what to do though. I am thinking about using a Mallory 4142 electric fuel pump with external bypass type regulator, which would let me dial in the pressure and retain the use of the rerturn line, which I believe will quiet the pump and keep the fuel cooler, among other benefits. Here is the pump and regulator:

http://store.summitracing.com/partdetail.asp?part=24118

What do you think of that idea?

yellow 72

7t2, when I first ran my Holley mechanical pump it was producing over 8 lbs.with the return line plugged and overcoming the float seats in my carb.
Insted of running a regulator, I threaded one of the bosses on the pump body for the return line and drilled a small hole into the pump chamber.
In other words I created a return outlet in the Holley pump where there was none. You can very the fuel pressure with the size of the hole. or you could even tap it for carb jets to change pressure :cheers: