750 Holley double pumper fuel pump advice.

[buddy350]

Currently running a holley 750 double pumper with vac secondary's and while out hotrodding around and jumping I noticed that the current holley Mighty mite 34gph 7-10 psi electric fuel pump cannot keep the carb full of fuel when at wide open throttle.

From day one the holley mighty might has barely been able to maintain 4 psi at the carb.


Anyone have any ideas?

I was thinking perhaps a Holley Blue 110gph 7psi pump and regulator part# 12-802-1




1986 Suburban
454 big block
speed demon air gap intake
Engine pro MC2004 hydraulic flat tappet stage 2 cam with roller rockers.
Heads are the old scool 290's with mild porting.

Manual transmission

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[Turbo4whl]

I am not familiar with either of those Holley pumps. I used a Steward Warner diaphragm type electric pump. 7 PSI for my Holley. The pump should be mounted low, close to the tank.

Problem is heat. Electric pumps don't like heat, and heat from the exhaust will shorten the pumps life. Even after adding a heat shield and insulating the lines the SW pumps just would not last.

I switched to a Holley block mounted pump and had no issues. Does your BB 454 have the provision for a block mounted pump?

 

[Brett77]

I just went through the mighty mite pump after my holly red went bad. All reads that it should work with 750 carb butt Holley said it should work in (theory) when I talked with a tech. It would fill the carb and start then stop running after short idle. I swapped out with new Holley red and works like a charm. I do have a mighty mite for sale if you want a second one.

 

[potent rodent]

red or blue will work , i believe the red does not use a reg and the blue does

 

[nvrenuf]

#1) A vacuum secondary 750 is a "dual line" (front and rear fuel inlets) carb but not a "double pumper" (front and rear accelerator pumps, mechanical secondary's) as that carb should only have 1 accelerator pump (on the front bowl).

#2) How do you know the fuel pump can't keep up with the carb? Are you able to monitor the fuel pressure under load at WOT ?

#3) What pressure regulator? Return type?

 

[buddy350]

Thank you

I have always understood that double pumper meant that fuel can be sprayed in from the front and rear regardless weather or not mech or vac secondaries.
I could be wrong and it would not be the first time or the last time.

We have a fuel pressure gauge at the fuel rail on the carb and it hangs out around 3 or 4 psi at idle, only reason I suspect the pump is unable to keep up is because when the motor starts dying at wide open throttle is that the fuel pump gets louder “ making the same sounds “ when there is no fuel in the pump.

I recognized this sound many times when I first got the motor running from the build.

that is the only proof I have that the pump cannot keep up.

as far as return line.
Yes
I’ve utilized the actual return line to the tank by Installing a return line style fuel filter and slightly crimping the return line male nipple to help keep up the pressure at the fuel gauge.

We added the return filter to help cut down on vapor lock in the hot Texas summer heat and it worked.

while out the other day mudding we completely closed the return line to aid in more fuel to the carb.

 

[potent rodent]

you need at least 6 to 7 psi at the carb