Question on fuel pressure regulator

[spstan]

I have a Holley spread bore carburetor. I've read where the Holley carburetors are very sensitive to fuel pressure and it needs to be around 6 psi (no higher than 8 psi) or the carburetor gets overloaded with gas. My mechanic claims you don't need a fuel pressure regulator if you have a mechanical fuel pump. But I've heard a lot of guys use a fuel pressure regulator on carbureted cars and why would Holley manufacture a low pressure fuel regulator? (unless the same guys are using an electric pump with a carburetor).

Does any one on this board use a fuel pressure regulator with a carburetor and mechanical fuel pump? I'm looking for a combination fuel pressure regulator / fuel pressure gauge. Paul

 

[Justin Plant]

First install a gauge in line between the pump and carb, to see where you're at. Go from there. If your car has a return fuel line off the filter or the pump, it almost certainly makes more pressure than the Holley wants. The upshot is, a regulator will work along with the return line.

 

[MEV]

I have both set-ups. I have an internally regulated performance mechanical pump on my 505/512. With an Quick fuel SS830 carb with no problems (with the factory 5/16 fuel line feeding it!) And i have a 496 chevy with an electric pump feeding the mechanical pump to an AED 950 carb again with no external regulator and no problems.

 

[CBODY67]

Consider that Holley was an OEM supplier of Chrysler and Chevrolet in the 1960s, plus a few Ford applications. NONE of them had any kind of external fuel pressure regulator as the normal mechanical fuel pumps would NOT exceed their pressure orientations. Using an electric pump was more for full-race situations or for cases n which a small booster pump was needed to help with vapor lock situations (usually on GM cars, as I recall).

Now, if you want to run some sort of mongo mechanical pump on your car, that's fine, but THAT might be when a pressure regulator might be needed. Or similar on a mongo electric pump. BOTH capable of supplying much more volume that the engine needs. On a stock motor, or one with some enhancements, IF you want to go to the trouble and expense of plumbing a pressure regulator, your call on that. Once you discover it's not needed, you might then re-sell it.

FIRST, read Holley's fuel pressure specs/recommendations in their manuals. As I recall, the pressure range is the same as a normal mechanical fuel pump. The main issue with fuel pressure is that it is not so great that it might over-power the float/needle and seat doing their jobs. Seems like the Holleys are spec'd at up to 8psi? Or is it 6psi? Usually more than any stock pump will produce, from what I recall.

Enjoy!
CBODY67

 

[57fury440]

There are carbs that use less pressure than your Holley does. It could be possible to need a regulator if that is the case, as you can get high pressure mechanical pumps. In your case if your carburetor works with 6 to 8 pounds of pressure, I think you would not need one.

 

[66 Monaco 500 365]

I ran a 440 with the stock Holley 6bbl setup in my original 383 Roadrunner, using the stock 5/16 fuel line and stock fuel pump with no regulator, the car ran to 5500 and ran 13.08 at 103.8
in my opinion you don't need any special regulator.
There are high pressure mechanical pumps that would need a regulator and electric pumps usually need one.
My $.02

 

[volksworld]

about 40 years ago i had a brand new Holley on my Chevy tow truck...and it would continuously overfill the rear float bowl and run like crap...i attributed it to the fact that i pretty much never kicked the secondaries in so no fuel ever got used up and hitting bad bumps might've bounced the floats enough to let in extra fuel...when i put in the big block i purposely went for an Edelbrock Performer cause it used a common float bowl for primaries and secondaries...i know a lot more now than i did then so in retrospect a pressure regulator (or at least bothering to check the pressure) might have cured the problem...on the other hand i've never had an issue with the Holley on my 440 in the last 23 years...

 

[spstan]

about 40 years ago i had a brand new Holley on my Chevy tow truck...and it would continuously overfill the rear float bowl and run like crap...i attributed it to the fact that i pretty much never kicked the secondaries in so no fuel ever got used up and hitting bad bumps might've bounced the floats enough to let in extra fuel...when i put in the big block i purposely went for an Edelbrock Performer cause it used a common float bowl for primaries and secondaries...i know a lot more now than i did then so in retrospect a pressure regulator (or at least bothering to check the pressure) might have cured the problem...on the other hand i've never had an issue with the Holley on my 440 in the last 23 years...

Volks; how does your 440 start? My 440 runs very good with a Holley spread bore when its running (almost like fuel injection). But sometimes its hard to start (belching white smoke through the carb throat and taking maybe 5-6 tries to start. I thought maybe a timing problem but my mechanic claims the carb is dumping fuel. Trouble is I rebuilt the carb (carefully) and I cant figure out where the fuel dump is, Accelerator pump looks dry and I re-tightened the carb mounting bolts. Ideas? Paul

 

[Justin Plant]

It's almost certainly the fuel itself. Gas isn't what it used to be. When an engine gets turned off, it'll heat up 30-40 degrees or more before it starts to cool back down. The fuel expands, vaporizes, and pushes itself up, out of the float bowl and down into the intake. Then your hot engine has to drink all that up before it starts. If everything is set up correctly, and tuned to a tee. I'd put my money on the gasoline. The mix of ethanal free gas still isn't anywhere close to the mix of gas when our cars were new.
Just a thought.

 

[spstan]

It's almost certainly the fuel itself. Gas isn't what it used to be. When an engine gets turned off, it'll heat up 30-40 degrees or more before it starts to cool back down. The fuel expands, vaporizes, and pushes itself up, out of the float bowl and down into the intake. Then your hot engine has to drink all that up before it starts. If everything is set up correctly, and tuned to a tee. I'd put my money on the gasoline. The mix of ethanal free gas still isn't anywhere close to the mix of gas when our cars were new.
Just a thought.

so Justin; what gas additive would raise boiling point of gasoline so it doesn't vaporize? Maybe some of that marine 2 cycle oil? Paul

 

[CBODY67]

IF the real issue is "a fuel dump", then when removing the spark plugs bEFORE starting the engine after it sits (cools off) a while, I would suspect there might be a few spark plugs which smell of raw gasoline? Even if it has evaporated a bit. Otherwise, look to see that the gap is accurate and teh plugs are clean of deposits and such.

As the accel pump feeds off of the bottom of the fuel bowl (on 4150-4160-4165-4175 Hollsy 4bbls), checking for accel pump shot is not really needed. It would take a lot of evaporation/percolation to empty any Holley fuel bowl, I suspect.

The secondary side has an idle system to keep fuel moving in the secondary float bowl. Just a very small amount of fuel, so what's back there does not get totally stale. An internal and non-adjustable situation, although there is a small set screw to keep the secondary throttle plates barely cracked, set at the carb factory and should not be changed.

Any fuel percolation usually goes out through the primary venturis, not the accel pump circuit.

The engine should not be back-firing through the carb, but they sometimes can with a hot engine. Especially with a Holley, whose power valve diaphram can rupture when such happens.

DO ensure the hot base timing is to spec, or just a tad above, for good measure. Maks sure it starts well cold and such. Then look at things which might change as the engine gets hotter.

Just some thoughts,
CBODY67

 

[CBODY67]

Ethanol'd fuel can be a bit more volatile (easier to burn), so decreasing the evaporation rate a bit with "oils" is not necessarily a good thing to do. Less evaporation-ability = harder to start, period. Which is where the ignition system comes in by making sure the sparks happen as they need to, in the first place.

Since we've had these same issues since the middle 1960s or so, with Chrysler products more than not, I can't help but wonder if the voltage to the coil might be an issue, when starting?

Enjoy!
CBODY67

 

[Justin Plant]

so Justin; what gas additive would raise boiling point of gasoline so it doesn't vaporize? Maybe some of that marine 2 cycle oil? Paul

No idea, Most additives have alcohol in them to dissipate moisture that may collect in the fuel. I don't know if you can raise the boiling point.

 

[volksworld]

at one point the 440's Holley began running rich...it also was an aftermarket dual feed Holley and it had one of those plastic foam floats in the secondary side...it had absorbed whatever crap is in todays fuel and was no longer buoyant...tried to replace it with a brass one but couldn't find one that would fit ...had an issue with a bad distributor pickup where i'd get no spark while cranking...that could cause it to flood if the choke's on and you're pumping the gas and there's nothing to light it...that one was intermittent and literally took years for it to happen often enough to troubleshoot