My GTX keeps vapor locking after I turn it off (fuel boiling out). I'm currently running a Holley mechanical pump, Eddy RPM Performer and Holley 750 DP. I have used an electric fuel pump before (Carter super pumper) and it was soooo loud, so I don't like it.

Can I put a "cheap" electric fuel pump in line with the mechanical pump so when I turn it off and the fuel boils out I can just flip a switch and turn the electric on to get it started? Will the mech pump let the electric pump through it?

yup

You can,BUT, if the diaphram in the mechanical pump were to rupture you'll have a mess.

How much would the cheap electric fuel pump restrict fuel flow when using the mech pump?

I'm not sure. I assume this is a big block car and you've tried the conventional approaches to the problem?

440 car. No, I haven't tried anything else. I can't do a spacer (air grabber hood). What else would help?

Insulating the fuel line(steel lines?) can be a big help. There used to be an aluminum heat deflector(thin) that the GM dealer sold for the 69 Z/28 (holley carb)that can possibly be a help. Jegs might have the same type piece. Jegs PN 510-108-70 is the same item.

I used to do this, but there are some issues. You of course should mount the electric near the tank. However, with the mechanical only, the restriction through the non-operating electric will cause a drop in the suction line, and could CAUSE vapor lock. You might be better off just running both all the time.

Your GTX is a '70? If so, you should already have the necessary vent lines to hook up a "vapor return" system like my six-pack had. I'm a HUGE believer in these. I don't remember the part no. but Wix (NAPA) should still make "universal" filters with a vapor return fitting. You simply mount the filter with the vapor return "up" and plumb the small line to a return line back to the tank.

If your car came with a tank carbon canister system, you should have a line already under there that you can "tap" into.

Also check for ANYTHING that can restrict the suction side, which will aggrevate the vapor lock condition.

Is the tank/ cap properly vented?

Are the suction hoses in good shape, and not collapsing?

Any chance the feedline is rusted, leaky?

How about the suction screen in the tank?

You should test the pump for proper suction (vacuum), pressure, and volume. Vacuum/ pressure test gauges just aren't all that expensive at any parts store.

he said to help with a vapor lock problem.. so yah it'll work. going down the 1/4 mile it'll work. continuous use,
it won't work.

Correct.

I have a Carter 4601 HP electric pump on my car with a recirculating system. On a quiet day, I can barely hear the pump running with the engine off.

This scare nonsense about pumping gasoline into the pan if the mechanical pump fails is silly--because--

The mechanical pump is no more prone to fail whether you have an electric pump inline or not, and--

If the mechanical pump diaphragm ruptures, it will STILL pump gas into the pan, whether you have an electric pump or not!!! You are just as likely "not" to notice the problem, either way.

The body of my old '70, as well as my '64 Polara 426 had thousands of miles on them this way, and I never had a problem.

yup,
I run 2 pumps on my charger,
also ran 2 pumps on an f250 years ago,
works fine.

there is ZIP, ZERO, & NOTTA need to run a auxillary fuel pump during normal cruising. so why take the chance?
BUT hey.. do what you want.

I don't know what these pumps are you guys run that are so loud. I put a walbro 255 in my brother's rampage. It's it's the hi-pressure version of the walbro 255, and an external in-line unit. It's the highest overall flowing 255 series pump made by walbro. And with the little dinky 2.2 running, I can't even hear the pump running. Someone has got to make a good flowing, low psi pump for carb apps that isn't overly loud. Run it with a return-style regulator and it'll both keep your fuel cold and evacuate any vapors out of your line. And it'll fill your carb bowls right back up before you even turn the key. Seems like a no-brainer to me if you've having evaporation and or vapor lock issues and cannot solve them.

I haven't used a mechanical pump since 1974. When you can afford to do it right get a good electric pump with a return style regulator. Throw the mechanical in the trash and drive anywhere you want. -Bob

Good info guys, keep it coming.

I think my problem with noise was my gas lines, not the pump. Let me explain, I had the pump mount isolated with rubber and actually hung the pump by plastic wire ties from the mount and the noise did not change. I can really hear it coming from the left rocker area (where the fuel lines are). I put rubber hose around the metal lines along the length of the car but that did not help. I think it the volume of fuel flowing through the lines that's making the noise, not so much the vibration of the metal lines. Maybe I should try another type of electric pump.

I don't have a regulator but I do have a return line.

Some electrics are noisy...the Holley Blue I had for one. That was a noisy brute. It was an older one , maybe the new ones aren't as bad. My new Mallory 110 is whisper quiet. I also have been running electric and mechanical for decades. Like someone mentioned, I go weeks sometimes without driving my car and I just let the electric fill the carb a few seconds and it fires up immediately. I also run the return line. No problems.