fuel pressure at 8psi

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mopardemon340

mopardemon340

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i have an issue with my fuel pressure.. i have a holley black electric pump and a qft bypass regulator. i cant adjust my pressure below 8 psi. i took the regulator apart and all was clean. fuel pump was clean and found to have no issues.. before we had good pressure but we had to change my fuel system and now this issue.. the changes we made was lower the fuel pump to level with the bottom of the fuel tank.. before it was higher and wasnt keeping primp. i also removed a fuel filter before the pump but plan on adding a new one once i order it.. so now im lose as to y my pressure wont go below 8. i have the regulator adjusted all the way out.. what could be the issue.. i have 5/16 lines for return and for feed. my carb is a QFT 850 double pumper
 
did your black pump come with a regulator? "...Fuel pressure regulator is required (recommend Holley P/N 12-704 for gasoline..."
Thats the screw I was speaking of. Does the QFT use a carb jet to regulate the pressure by restricting the return side? Maybe try a larger jet or remove it completely for testing. you could probably just drill it out if you dont have jets handy IF it uses a screw in jet. ALSO "...It is advisable to use the same size return line as the feed line from the fuel pump to be certain the return line can handle the same fuel volume as the pump output. If the return line is too small it will not be possible to reduce the fuel pressure to the desired level..."
 
My qft regulator dosent have a jet its wide open unless the jet is the brass nipple like piece? Both feed and return are 5/16 line. No idea how much they can flow. never had an issue until I made the changes stated above.
 
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Do you have at least a 3/8 fuel line to feed this deal? I have a Holley 125 HP with a 3/8 line and no regulator needed, i have 7 psi and it holds at 5 psi flat out.
 
That may be too small. I had an SX EFI pump and regulator that would adjust to 5 psi. The key was i needed a #10An feed and a #8 return line. I tried to cheat with smaller lines and could not get it to go below 10 psi.

Please dont be offended, as i dont know you? You have the lines going to the correct ports on the regulator? As i said the smaller line may be causing you issues. I dont think that small 5/16 line is going to supply the volume of fuel needed for your application. You may end up running a new 3/8 or #6 An line from the rear to the front. I ordered a fuel tank pickup with a 3/8 pickup and then plumbed that to the pump, then ran #6an to the carb. no issues.
 
Fisher said:
That may be too small. I had an SX EFI pump and regulator that would adjust to 5 psi. The key was i needed a #10An feed and a #8 return line. I tried to cheat with smaller lines and could not get it to go below 10 psi.

Please dont be offended, as i dont know you? You have the lines going to the correct ports on the regulator? As i said the smaller line may be causing you issues. I dont think that small 5/16 line is going to supply the volume of fuel needed for your application. You may end up running a new 3/8 or #6 An line from the rear to the front. I ordered a fuel tank pickup with a 3/8 pickup and then plumbed that to the pump, then ran #6an to the carb. no issues.
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Yup it's all plumbed correctly. what do you mean you had to use an10 and an 8. What size are those? 3/8 is 6 correct
 
OK, so your in and return are the same size. How do you have is plumbed, before or after the carb? That is a boost referenced part number? Does the screw do anything to the pressure? 3/8 = 6AN (think of 1 AN as 1/16 of an inch)
 
pishta said:
OK, so your in and return are the same size. How do you have is plumbed, before or after the carb? That is a boost referenced part number? Does the screw do anything to the pressure?
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The top screws adjusts the pressure. and its before the carb. It's not a boosted regulator.
 
mopardemon340 said:
The top screws adjusts the pressure. and its before the carb. It's not a boosted regulator.
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Every pressure reg I`ve ever used, I plumbed at least 3/8 in to the bottom port, then out the dual ports to the carb. Most of the time I ran `1/2" or -08 to feed the bottom inlet. This was all before switching to fuel inj. , now it`s 43 pounds of pressure.
 
My mistake, the generic QFT feasture list includes all part numbers. Does yours have the: "....Adjustable by-pass jet for tuning low rpm fuel pressure or unrestricted by-pass"? It looked like one of the models had a carb jet screwed into the outlet and Im only guessing that it would alter the fuel pressure. QFT says its adjustable down to 1.5psi? The cheapo Mr Gasket fuel pressure regulator that I have was just a series of smaller holes and a knob so Im assuming the carb jet may have an impact on the pressure.
 
pishta said:
My mistake, the generic QFT feasture list includes all part numbers. Does yours have the: "....Adjustable by-pass jet for tuning low rpm fuel pressure or unrestricted by-pass"? It looked like one of the models had a carb jet screwed into the outlet and Im only guessing that it would alter the fuel pressure. QFT says its adjustable down to 1.5psi? The cheapo Mr Gasket fuel pressure regulator that I have was just a series of smaller holes and a knob so Im assuming the carb jet may have an impact on the pressure.
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This is what it looks like inside. There is no jet only this brass piece that blocks off or opens up the return hole. theres nothing in the return hole

20180527_170615.jpg


20180527_170611.jpg
 
I was trying to explain this jet if your had it on any leg? The video said this was a return model. I dont know why it would have this if it were not to restrict something. Dead head option would have a plug here.

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View attachment 1715180744

That ball is the valve seperating full pressure in and regulated pressure out. IIRC, the fuel pressure coming in wants to unseat that ball and flow past it. The spring on top is forcing the ball to seat onto the fuel port, eventually the pressure will unseat it and fuel will flow. The spring pressure can be adjusted for more or less seating pressure. The boost reference barb just injects high boost pressure into the spring cavity to simulate a higher tension on the regulator spring for higher fuel pressure under boost.
fpregv3.jpg
 
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I'd suspect the spring is not relieving tension on the check ball diaphragm? Only way relieving spring tension via the CCW rotation of the screw (out) would lessen fuel pressure would be to relieve the bypass port check ball tension, sort of opening the bypass port to relieve carb pressure as in a oil pump relief valve. Im stumped not having it in front of me.
 
I got the adjustment screw backed out all the way. I'll try and see if I can get pictures of the entire unit apart
 
I've not seen where you say you actually have a return line. Unless I missed it. Are you dead heading a return type regulator?
 
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