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Return fuel line size
beachbuggy61 - December 5th, 2010 at 02:48 PM

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


66brm - December 7th, 2010 at 04:30 PM

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 - December 7th, 2010 at 04:51 PM

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.


beachbuggy61 - December 7th, 2010 at 09:51 PM

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.


66brm - December 8th, 2010 at 11:35 AM

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 - December 9th, 2010 at 04:23 PM

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.