Return fuel line size

beachbuggy61 Seriously Crusin Dubber

162 posts · joined Dec 2009 · 5 Dec 2010, 2:48 pm

#815680

Howdy.

I've finally got around to setting up the holley blue fuel pump with the malpassi rising rate regulator to ensure I have fuel pressure 3lbs greater than boost. All good.

Now for the problem. With my old solid state facet pump (max 4lbs or so) in the system, I can adjust the pressure with the regulator anywhere from 1 to 4lbs easily, and when I set it to 1 lb, I can hear the excess fuel running into the tank via the return line. However, when I put the Holley pump into the set-up, it blows the pressure over 15lbs even with the regulator turned all the way down!

I've run a new supply line through the tunnel (5/16") line, and am using the old supply line (I think they're 1/4") as the return line.

I'm at a loss. Is the return line too small perhaps or is there something wrong with the pump? I'm sure the regulator's ok and the fuel pressure gauge, because I can adjust pressure easily with the facet pump.

All help appreciated.
Thanks, Marc

Baja
1915cc's of raw power 🙅
Turbocharger
Intercooler
EFI
Crank fired Ignition
Runs E85
Engineered

"The Lord does not subtract from the life of a man, the hours spent on his Volkswagen" Anon.

66brm Seriously Crusin Dubber

140 posts · joined Nov 2009 · 7 Dec 2010, 4:30 pm

#816015

Where does the stock line return to the tank?, it sounds like you have some sort of restriction in there, a filter or dodgy flex line? What are the specs on the new pump ie flowrate @....psi?

Sides Veteran Volks Folk

2,220 posts · joined May 2007 · 7 Dec 2010, 4:51 pm

#816017

Everything I've ever read says return line should be the same size or larger as the supply line.

http://go.mrgasket.com/pdf/TS_FuelSys.pdf

My understanding is if the return line is too small then the regulator just can't bleed the pressure off quick enough, which sounds exactly like what you've got.

VWDCQ vice pres & web dude - vwdcqinc.org.au
Join a car club - get car peeps

My toys
'70 Hillclimb Bug 'Jezebel' w/- Haltech EFI - http://bit.ly/VwTNtQ
'60 KG Coupe - resto kinda started
01 New Beetle - gf's car, but I turn the spanners

beachbuggy61 Seriously Crusin Dubber

162 posts · joined Dec 2009 · 7 Dec 2010, 9:51 pm

#816066

Thanks Dave, you're dead right I've since discovered. I put a 5/16" line on the return of the regulator and ran it into a bucket just to see if that would fix it and I was able to set the idle pressure perfectly at 3psi.

Now all I have to do is run ANOTHER 5/16" line from front to back for the return and ignore the original line altogether. I thought it was fairly easy threading the first one through past the pedal set and the other bits and pieces inside the tunnel.... a second one is going to be real fun! Wish me luck.

Thanks again for your advice.

Oh. 66brm, the return line feeds into the top of the tank, I've mounted a 5/16" bulhead fitting in there.

Cheers, Marc.

Baja
1915cc's of raw power 🙅
Turbocharger
Intercooler
EFI
Crank fired Ignition
Runs E85
Engineered

"The Lord does not subtract from the life of a man, the hours spent on his Volkswagen" Anon.

66brm Seriously Crusin Dubber

140 posts · joined Nov 2009 · 8 Dec 2010, 11:35 am

#816099

Cool, hope you get it sorted, I'm just about to tackle the same job on my oval, 5/16 feed and return but for a 2176 efi donk

beachbuggy61 Seriously Crusin Dubber

162 posts · joined Dec 2009 · 9 Dec 2010, 4:23 pm

#816305

All done! The second 5/16" line went through a breeze. Just had to cut an extra hole at the back for it to come through. Fired it up, pressure good at 3 psi and we're away.

No I just hope it does as advertised and gives me correct pressure under boost!

Marc.

Baja
1915cc's of raw power 🙅
Turbocharger
Intercooler
EFI
Crank fired Ignition
Runs E85
Engineered

"The Lord does not subtract from the life of a man, the hours spent on his Volkswagen" Anon.