Guys I'm at a point with fuel psi that I'm stumped. Dual carb setup on alcohol running a Magnafuel 500 pump and Magnafuel dead head 4 port regulator. Engine is a 440 SBC made 780 and runs 6.0s in a 3500lb nova. I can set the fuel pressure at 3.5 lbs and adjust floats anywhere i want, if i set pressure at 4 lbs and try to adjust floats you can try all day setting the floats and the N&S want seal off and just keep creeping up until it floods over. Before anyone says i need a belt pump I’ve had 2 on the car this year and have a bad lean spike and the electric got rid of that.
3 non liquid filled gauges and racepak sensor all says the pressure is right. Pump out of the box set at 28 psi but pushing 32 with 16 volt battery. I put the light spring in and drilled the bypass hole to 3/8 per Magnafuel set at 20 psi and it cant keep up with the low pressure from reg to carbs and doesn’t change the pressure issue with the N&S. Running the pump at 32 and 3.5 psi the car is consistent but on the edge of sucking air to the jet and AF shows it does sometimes. Ive upped pump to 38 psi and the same 3.5 psi to carb hoping it gets rid of it almost running out each pass. Things I've tried

New .150 N&S 3 sets (2) Holley (1) BLP
New .130 N&S Holley
Areomotive bypass regulator
Holley dead head regulator
Magnafuel dead head regulator
Plumbed regulator to carb -6 and -8 lines. Has -12 to pump and -8 pump to regulator, pump and tank up front
Bowls that came with carbs Billet, tried different floats
APD Billet no foam bowls with there floats (all wedge floats used)
Pump psi 20,32,38

Anyone had, seen or heard of this before ?

Now to the ones who say i need a belt pump
I started the year off with my Rons billet 0 pump, transbrake release AF would go to 4.8 then 6.0-6.2 as soon as the rpm graph would start across then go so rich the car would nose over, could lower psi and get down the track but it would go so lean at the hit I wasn’t willing to run it and hurt parts. I bought a Waterman .500 pump and same results, i tried 3 regulators, replumbed 5 ways tried an APD internal bypass pump. I do think the 150 N&S are to big with the belt pump and putting .110 or .120s and set the idle psi and wide open psi closer together would fix the lean spike and flooding the car after it leaves if i could run any pressure at idle and the reason i say that i tried duel N&S bowls on a single carb on alcohol and had to have .110 N&S to run or it would do the same thing. So for now just trying to figure out why the N&S won’t hold over 3.5 without bleeding over

I'm wondering if a bypass/return regulator would help? Or two, one on each carb.

BLP bypass regulator.

Just made everything up and fired the car tonight. Fuel pressure set 3.5 psi at 1200 rpm per BLP instructions.

Change your floats, they are probably heavy and running out of adjustment.

Bypass regulator plumbed after the carbs. Line from pump to a log that feeds carbs. Bypass line off log to inlet of bypass reg. Return line from reg to tank.

quote:

Originally posted by Curly1:
Change your floats, they are probably heavy and running out of adjustment.

THIS…

If all bowls are flooding then I don’t really know other than floats but if only one like I had it turned out to be dried out and cracked o ring on needle and seat assembly.

I don't know if it's part of the equation or not, but I see you have the -12AN feeding the pump, but only have -8AN from pump up to the regulator.. The amount of fuel the Magnafuel 500 flows, it could have something to do with the smaller feed line into the regulator.. Just food for thought. I think the pump instructions say they want a -12 into pump, -10 out of pump into the regulator and then from there can split it down into your -6 or -8 to a fuel log or the bowls.

I have ran a similar setup -Areomotive A-2000 pump -10 to pump -10 to regulator Areomotive "soft-seat 2000 4 port -6 to carbs dead headed no return .150 holley n/s 7lbs. fuel pressure but a smaller 358 inch engine w/2 750 Rupert carbs-no issues key maybe in -10 line from pump to regulator

Sorry just saw where you had already changed floats. A smaller N&S will hold more pressure and with dual carbs you should not need the large N&S at that power level. More pressure at the N&S may help but I do not think it will resolve the problem.

Possibly? the type float you are using. It seems to me if you have a regular float on a SIDEWAYS mounted carb when you accelerate the fuel will go to rear of bowl and may prevent the float from dropping allowing N&S to let fuel in. May need some floats tapered up towards rear of car. Your motor probably has a little downward rake in the rear, then g forces on the fuel at the hit and most of the fuel ends up on rear of bowl (which is rear side on sideways mounted) trying to raise float when you need fuel the most.

I would call someone like Reher and Morrison and ask them about the floats for dual sideways mounted carbs.

When you run the mechanical pump you can have bypasses that open up where ever you want and pull off as much fuel as you want. Actually there is no reason you could not do the same with the electric pump but I do not think it should be that touchy on fuel pressure. I think the problem may be related to float type. Also I would not run a Deadhead regulator on anything but do not think that is the problem here.

I've been running this regulator for a long time. Seems to work but I do run a belt drive pump.

https://aeromotiveinc.com/prod...00-bypass-regulator/

Correction on line size. It does have a -10 pump to regulator. Floats are the wedge floats for sideways mounted. I’ve also tried .130 N&S with no change. Anything I could think of if tried and no change at all

One other thing but don’t know if it could cause this is there are different length meddle and seat assemblies and maybe you got wrong ones and are putting you at the edge of adjustment. I found this out this past spring, my carbs have longer ones than stock Holley but don’t remember exactly how much longer. The short ones I could not adjust enough to keep from flooding. According to Holley they only make one length so apparently builders are making their own and different length. I have two sets of carbs and both have the longer ones. One set that Prosystems last worked on and a set of Get’m garage carbs.

How big of a tank vent for air inlet do you have-did see that being and issue on anothers car before-mine is -10 rollover valve-just a thought

Here is a dumb question, are you trying to set fuel pressure and float levels with the car running or not running? I would assume being alcohol, these are the stainless needle and seats?

When I first put on our APD billet 750 and went to set fuel pressure at the recommended 7 psi, it kept blowing past the needle and seat and coming out the vent tubes. I called APD and they told me that with the stainless needle and whatnot, that you had to have the car running and drawing fuel to check and set the float level. Weirdest thing I had ever heard but fired the car up, got the float and pressure set and haven't touched it since 2 years ago.

Few things to look at,,,

First you should not have issues at 4 PSI, something is wrong even with w .150" diameter N&S, especially just sitting in place at idle. Have you checked your gauge?

Next, there is no reason to use a .150" N&S with two carbs with only 780 HP. So you have an issue somewhere. .130's are good. It doesn't matter what kind of fuel pump you use!

Is the fuel tank in the rear of the car, this would likely cause a lean spike with the belt drive pump unless you have a surge tank in front of the motor.

If you are using the black bowl floats, they will absorb alky and get heavier as others mentioned. Over time this will cause the float to rise until it causes a problem, most reset the floats and move on, you may get away with this but sooner or later you will reduce float drop too much which will cause a fuel flow restriction at the N&S causing the bowls to drain on a run and lean out the motor! When you lose too much float drop the needle can't drop far enough to clear the seat causing the flow restriction!

Electric pump high side fuel pressures general rule, set it at 3 to 4 times your idle low side fuel pressure or 18 to 25 PSI.

I’ve got an idea, run it on gas and put all this bullshyt and expense behind you.

-8 vent even tried a -10 vent
Car is running when I set pressure and yes stainless N&S
Car as done this all year with new carbs, and new bowls/float and another new set of floats
I’ve had .130 in it and no change. I do agree I don’t need the .150s if the pressure was up a think I could get by with using .110 or .120s
Tank is in the front with the belt pumps and the electric.
I’ve tried 2 Holley small non liquid filled gauges, auto meter 2 1/6 gauge and my racepak sensor and all the gauges read the same with the racpak reading 3/4 pound lower.
And no ED I’ll never swap back to gas. Been running alcohol carbs and injection for 25 years and no desire to change back to gas.
Don’t get me wrong the car has been good all year running the low pressure with the exception of the air fuel going lean maybe 1 in 20 passes and I think turning the psi up from 32 to 38 on the pump will fix that issue but drives me crazy trying to figure out why it won’t run 4 to 6 psi.
Maybe it’s something in the carbs and I’ll know that next week as I have 2 new APD 950s on the way to replace the 1050s that I have now

Dave the only thing I haven’t tried to this point is two regulators. One to each carb and that may be what it needs but to me pressure is pressure but at this point what’s two more regulators gonna hurt to try. If anyone needs a new/uses 2-3 week regulators I think I have 3 deadheads and 3 bypass I’d sale cheap.

Your time, your $, your car but I know that you’re making it harder then it needs to be and you’re struggling, proof is this thread and you’re no more consistent nor competitive on alky so why do it?