Gun Jam

I had a carter mechanical fuel pump that I broke by over-tightening a fitting. I replaced it with a holly mech fuel pump. The holly has always been sketchy typically the fuel pressure is at 6lbs but does weird things sometimes it will drop off very low at idle or city street cruise speed down to 1 or 2 lbs and then creep back up as well as cause fuel pressure flutter in the gauge when cold or at random times and then goes away. The fuel gauge is mechanical and reads right off the carb pick up line at the carb.

I am planning on replacing the holly fuel pump with a new carter mechanical pump the question is...If I wanted to achieve the smoothest most consistent fuel flow possible to the carb could I do that by including a fuel pressure regulator? If I did run a regulator I would want to make sure the fuel pump produced more pressure than the highest setting of the output side of the regulator...For example 7.5 psi in (lowest) with 6.25 psi out (highest)...right?

It seems to me that a regulator would reduce fuel pressure flutter or spikes and would output a much more consistent fuel flow..

Thanks

-Gun

67mustang302

Yes, and yes the pump pressure needs to be higher than regulator pressure...otherwise the regulator will only control pressure spikes, not drops. You want a pump with pressure that regardless of fluctuation stays above the pressure you want, and the regulator is always regulating it down.

If you have the money and don't mind re plumbing, you could go electric. Not necessary for a carb, and more expensive, but has some advantages.

Gun Jam

Thanks for the input...I have the money but prefer to avoid electric pumps. Do you have a recommendation on a high quality regulator? It must absolutely not be a POS and should last many years of daily driving.

Thanks

-Gun

67mustang302

I ran a quick fuel before, never had issues with their reg. Holley's are prolly fine too. These days I pretty much run Aeromotive for most fuel bits (pump is a Walbro and reg is the FAST one on my XFI setup).

http://aeromotiveinc.com/products-pa...ted-regulators

Gun Jam

Those were the ones I was looking at...why two outlets? Does one simply plug the unused outlet port?

Im thinking this one right now

http://www.summitracing.com/parts/aei-13205/overview/

Thanks again!

Gun Jam

with one of these fuel pumps

http://www.summitracing.com/parts/cr...view/make/ford

http://www.summitracing.com/parts/ed...view/make/ford

http://www.summitracing.com/parts/cr...view/make/ford

Of these the edelbrock seems to be the most suited for the application but im not sure of its quality. Could I pull out the AN fittings on the carter and use standard pipe fittings like I have now?

67mustang302

I had an Edelbrock mechanical before, it seemed to produce really consistent pressure even without a regulator, right around what it said too. Never had issues with it. Their carbs suck for performance but their quality is pretty good.

I think most of the regs run 2 outlets for dual carb? Maybe for mounting issues. Not sure honestly, but it seems to be pretty standard. Just plug the one you're not using.

Al Newman

Not really sure that consistent fuel pressure via a mechanical pump is all that important with a carb. The pressure might drop off or flutter when the needle and seat opens to let fuel in the bowl, but as long as the bowl doesn't dry up during operation, the carb could care less what pressure is being presented externally. EFI is a whole 'nuther animal.
Best, Al

Gun Jam

Al I would agree with you for the most part but somethings up I suspect the fuel pump because its been that way right after I changed it. Ill be rolling along and notice some engine stumble and look over the gauges to find fuel pressure at 0lbs. Back off for a second and it starts to climb back up. Is not even under load it can do it at idle too.

Also float level will change with pressure too if you are getting large pressure differences it can cause inconsistent carb operation causing main circuits to come on at different times due to float level change

So since I dont like the way the fuel pump is acting now I might as well redo the system so it provides the most consistent output I can achieve.

Thanks!

-Gun

67mustang302

Fuel pressure matters with a carb. The flow through the needle/seat changes at any given float position as pressure changes. Fuel level in the bowl/main metering well determines how the metering circuit of the carb mixes fuel. Fluctuating fuel pressure causes the fuel level to move around where it shouldn't be.

how much it matters depends on the carb/engine setup.