[David Jones]

Originally Posted by Holeshot71

I'm considering doing this at some point. When you're driving normally with the pump off does your mechanical pump just pull fuel through the electric pump or do you have some kind of bypass?

Mine pulls through the pump.

[ponyakr]

Originally Posted by David Jones

Mine pulls through the pump.

Don't know about ALL pumps. But the mechanical WILL pull thru that Carter elec.

https://www.ebay.com/p/Electric-Fuel...4070/191388380

[Keith Seymore]

Originally Posted by David Jones

I too suffered through fuel starvation with mine, but only right up toward the end of a 1/4 mile run. At that time I ran a "deep sump" type mechanical fuel pump. It did fine on the street, I don't ever remember issues with fuel in a street situation. I'm sure I could have cured it other ways but I bought a Carter P4070 electric and mounted it to a piece of aluminum angle that I installed between the gas tank strap bolts. If I see that I'm going to hammer on the car, I flip it on. Day to day driving, I keep it off. I also find it useful to prime the system with when the car has sat for a while.

This is basically my setup on both the GTO and the Chevelle (Holley electric at the tank, mechanical pump on the block) for the last 40 years or so.

Drive around on the mechanical pump; flip the electric pump on during the burnout and for the duration of the quarter mile run.

K

[Holeshot71]

Interesting, do you find any starvation issues if you happen to run it hard without the pump on? Also do you guys run some kind of filter before the pump or just the stock sock?

[ponyakr]

Will run out of gas pretty quick, after WOT. Ask me how I know.

Yes, I have forgot to turn the pump on.

After that, I began flipping it on, after the burnout, but just BEFORE pre-staging.

I ran an inline filter(3033 NAPA/33033 WIX) before the pump, and another just before the carb inlet, but didn't run an inlet filter. I realize that this is not the way most do it, nowadays.

[David Jones]

Originally Posted by Holeshot71

Interesting, do you find any starvation issues if you happen to run it hard without the pump on? Also do you guys run some kind of filter before the pump or just the stock sock?

It will run out of fuel in late 2nd gear when running hard using just the mechanical. I ditched the tank sock and have a 40 micron RobbMc canister before the electric pusher and still run a long Q-jet filter in the carb inlet.

[Holeshot71]

Thanks for the info! I'm not planning on doing any racing with this car but when I run it hard through the gears it starts to feel flat at the top fo 3rd. Plus I like the idea of filling empty fuel bowls after sitting for a few days and maybe hot soak/starts.

[Tom Vaught]

This picture is a very close copy of what I did years ago with a Holley Blue Pump and a High Volume mechanical pump. "Electric Fuel Pump Bypass"

Tom V.

[Skip Fix]

My Mallory 140 would not pull through. Years ago on my 409 Impala it would through the Carter electric. Heck I bypassed the mechanical to avoid one more source of heat soak anyway.

[jarretts70]

Thanks for all the input. Glad to have Cliff chime in, I followed his book when rebuilding the carb. This stumble aside the car runs excellently.

I originally rebuilt the carb with the stock fuel inlet seat (.125? Not sure...). I have since upgraded to a .130 seat. However, I should note I never actually measured it. It came in a packet labeled .130 & I just swapped it in..It made no difference.

I noted earlier that the Holley mech pump made it worse. I'll elaborate & see if it helps troubleshoot: With the stock type fuel pump the car would accelerate HARD when going to WOT - either from a dead stop or from a roll.

After changing to the Holley pump it does not accelerate as hard. It's still quick, but not near as hard hitting as before. I I'm guessing that it has to do with the fact the Holley pump has a smaller bowl? Or it's just not what it's cracked up to be. Or I'm missing something else.

I also will note it does not matter if the gas tank is full or not, so I'm guessing that the level of the pickup in the tank is not the issue. I've been thru the lines front to back a few times looking for a kink or restriction & I think it should be all good.

My current plan is to start by dropping the tank to make sure the pickup is not clogged or damaged. Sending unit for the gauge is kind of wonky, so its a good reason to drop the tank. If that doesn't help next up will be to rig a fuel pressure gauge..

[ta man]

Originally Posted by Tom Vaught

This picture is a very close copy of what I did years ago with a Holley Blue Pump and a High Volume mechanical pump. "Electric Fuel Pump Bypass"

Tom V.

Well engineered!

[Tom Vaught]

Thanks, I did another one where I used copper pipe fittings and silver soldered the pieces together. So the components were lighter and also a lot less chance of a leak in one of the fittings. The flow was improved vs using the machined threaded brass blocks.

The check valve mounted a bit lower though but it was still tucked into the upper area above the rear axle.

Tom V.

[Holeshot71]

Originally Posted by Tom Vaught

This picture is a very close copy of what I did years ago with a Holley Blue Pump and a High Volume mechanical pump. "Electric Fuel Pump Bypass"

Tom V.

I always thought you needed some sort of bypass but wasn't sure how to plumb it. A picture is worth a thousand words. I assume the blue canister is the check valve?

Originally Posted by ponyakr

Will run out of gas pretty quick, after WOT. Ask me how I know.

Yes, I have forgot to turn the pump on.

How about the opposite, say you leave the pump running for an extended amount of time just cruising around. Will the mechanical pump have any issues? I'm running a deep canister pump with a return.

[ponyakr]

"...say you leave the pump running for an extended amount of time just cruising around. Will the mechanical pump have any issues? I'm running a deep canister pump with a return."

Can't see how a low pressure elec pump could harm a mechanical pump.

But, the experts here may have a different opinion.

[Cliff R]

"I originally rebuilt the carb with the stock fuel inlet seat (.125? Not sure...). I have since upgraded to a .130 seat. However, I should note I never actually measured it. It came in a packet labeled .130 & I just swapped it in..It made no difference."

Too small for what you are doing. The stock seat was bigger than .130". When you get time PM or email me and we'll get some better parts in that carb for what you are doing.......Cliff

[Tom Vaught]

Originally Posted by Holeshot71

I always thought you needed some sort of bypass but wasn't sure how to plumb it. A picture is worth a thousand words. I assume the blue canister is the check valve?

How about the opposite, say you leave the pump running for an extended amount of time just cruising around. Will the mechanical pump have any issues? I'm running a deep canister pump with a return.

A couple of things to think about with Fuel Pumps and Engines.

1) Old Ford Model A and T engines did not use Mechanical Fuel pumps to feed the carburetor fuel. They used a high mount fuel tank and used GRAVITY FEED to feed fuel to the Carburetor. The engines were only a few Horsepower so that Gravity Feed worked ok.

A co-worker one time had a fuel line failure on his vehicle. We were working afternoon shift in the Emissions group. No way to get it fixed at a shop and he had to get home to take care of his mother. So we hooked up a hose from a 5 gallon Jerry Can to the carb, passed the hose thru the front of the hood opening so it was on the safety latch position, taped the Jerry Can to the hood, and fired the car up.

He could run about 20 mph before the engine would consume more fuel vs the flow from gravity feed and start to sputter. Traveling back streets and roads he made it home fine.
Took him a couple of hours to get home. But he made it.

So the point is you use the mechanical fuel pump to do two things:
Raise the fuel to the carb with the carb being higher vs the fuel tank.
Provide negative fuel pressure to remove fuel from the tank (using atmospheric pressure) 14.7 psi to push the fuel forward to the fuel pump and the using the pump to lift the fuel to the carb. That is why you need a good vent on the tank.

With a By-pass Circuit and a low pressure higher volume fuel pump, you can feed the mechanical fuel pump just fine to support a typical street engine.

Trans Am engines in the old days rarely needed more than a pair of the old Blue pumps to feed the race engines. One always running, one for a back-up if the main pump failed.
They did not both run at the same time.

All the pumps out there do a lousy job if the needle and seat(s) are the wrong size/design for the fuel demand of the engine.

Tom V.

[Keith Seymore]

Originally Posted by Tom Vaught

1) Old Ford Model A and T engines did not use Mechanical Fuel pumps to feed the carburetor fuel. They used a high mount fuel tank and used GRAVITY FEED to feed fuel to the Carburetor. The engines were only a few Horsepower so that Gravity Feed worked ok

Tom V.

This is also why Model T owners would sometimes need to turn around and back up a steep hill...

K

[David Jones]

Originally Posted by ponyakr

"...say you leave the pump running for an extended amount of time just cruising around. Will the mechanical pump have any issues? I'm running a deep canister pump with a return."

Can't see how a low pressure elec pump could harm a mechanical pump.

But, the experts here may have a different opinion.

I've run my electric for hours with no issue. It's now a bit over 10 years old. My mechanical also has a return.

[TAQuest]

Something funny going on here. All of y'alls cars should run on one high volume mechanical pump.
I ran two in tandem once as a precaution only because I was running nitrous at the track and fuel starved means an explosion.

[242177P]

Originally Posted by TAQuest

Something funny going on here. All of y'alls cars should run on one high volume mechanical pump.
I ran two in tandem once as a precaution only because I was running nitrous at the track and fuel starved means an explosion.

As usual, you don't have a clue.