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Old 05-10-2019, 08:16 PM
eric32 eric32 is offline
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Holley billet fuel pressure regulator issue.

Hello guys I am starting another post and I am having some weird issues and tried to research things and I can't come up with anything. I just hooked up a carter mechanical fuel pump in replace of my electric in line fuel pump.

I have a holley 12-841 billet fuel pressure regulator that has a bypass line and adjust from 4.5 to 9 psi. I finally had everything plumped up today and gave it a start and the fuel pressure was at only 3 psi and my gauge is on my fuel rail at my carb and not on the regulator which has a gauge port for one. I tried adjusting it to give me about 5 psi and no matter how much I adjusted it the thing would not go over 3 psi and if I tried to lower it then it would go down to almost zero but I left it up as high as 3 psi.

When I squeeze my input hose coming from my fuel pump into the regulator it will make it bump up just a hair if that means anything. I even tried to squeeze my return line off just to see if it would change anything and nothing it still stays steady at 3 psi. I took it out for a drive and it seemed to not be starving for fuel and even on the highway at cruising speeds and giving it some gas it does not seem to run out or anything.

With my previous electric fuel pump even with the return line it started up at 6 psi then would drop way down when it got hot then it would just go to zeo and my lines are routed away from any heat source and I think my electric pump maybe was just going junk.

My mechanical pump is a carter series m4685 and says it puts out 7psi according to summit and I ran the same pump on my last build with no regulator and my pressure gauge would fluctuate betweent 4 to 7 psi as the pump would work. Could there possible be a difference in the reading of the psi from the regulator port vs the port on my carburetor fuel rail? 3 psi is pretty low and I know my engine would not last long if I really got on it for a long enough distance. I have already thrown a lot of money at this thing and now this mystery. Anyone hear of this before. All lines are nice and routed good and no restrictions.
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