[Shiny]

Originally Posted by carbking

I have been forced (reluctantly) to install electric fuel pumps on ALL my older vehicles because of the panther-pxxx currently being sold as gasoline.....
Jon

Originally Posted by Kenth

I have found fuel "drain-back" thru fuel inlet is a myth.
Fuel evaporation is not, as the carb is 100% vented to atmosphere.
....

FWIW

Originally Posted by Radman

I ended up putting an electric fuel pump just in front of the gas tank on both of my Pontiac's. ....

Originally Posted by Kenth

...
In addition, all mechanical fuel pumps have a check valve that prevents fuel from "flowing back into the tank".

FWIW

I'm a believer in evaporation being the dominant source of loss and significant enough to be a PITA after only sitting a day or two.

I also know the mechanical pumps have a built-in check valve.

IIRC, the stock filter at the carb inlet also has a check valve, correct?

Regardless, I think I've asked before but what specific electric pumps are used for this? I suspect I will want one.

Mike

[Schurkey]

Originally Posted by Kenth

all mechanical fuel pumps have a check valve that prevents fuel from "flowing back into the tank".

Some pumps have two check valves--one inlet, one outlet.

Some pumps have six check valves--multiple inlet, multiple outlet for higher flow volume. No doubt over the course of automotive production, there's pumps with other numbers of check-valves.

It's entirely possible for them to not seal completely. Even slight leakage of an inlet and outlet will drain everything from the needle valve to the level of the fuel in the tank, given enough time.

Thus my suggestion to connect a vacuum pump to the inlet of the fuel pump, to see if--or how badly--the inlet check valves leak.

[grivera]

Originally Posted by Shiny

grivera - does a 69 have a return line from the pump to the tank?

Mine does not have a return line. Also, I have a vented gas cap which someone mentioned shouldn’t be. Not sure if that has any effect on my situation. I’ve been working on the 66 so didn’t get time to mess with this today other than getting that picture.

[HWYSTR455]

I know some caps have vented printed on them and they don't vent for chit.

I know many have converted on earlier cars to an external vent/separator, and have reported improvements, but can't give specifics on that. Most I've seen make those remarks don't provide data.

The Rick's tank I got came with a neck that has the late model type baffle and cap that ratchets when tightening, that I am fairly certain isn't vented. I run an OE type separator/vent so don't really care. The way I have it setup it has like 3 5/16 vents that are open to atmosphere, and I have no smell or vent issues.

I've tested free-flow on the last 2 tanks trying to troubleshoot a delivery problem, at the end of that I know I have zero delivery/vent problems.

My issue was a fluttering relay that was going bad, and figure that out by fluke. Friggin cost me a couple tanks, multiple pumps, and a handful of filter elements. The Rick's tank pump hat comes with a twin pump harness, and when I installed the tank I went ahead and upgraded my wiring to two 10g feed wires and a pair of 70a relays. I just happened to swap the relays around and my issue went away. Scratching my head, I tried switching the relays back and the problem came back. Pitched the one relay and all is good.

Granted, it started with gas I got at a station that had a ground pump brown out, and it pumped tons of metal particles into everyone's tank for a couple weeks. They eventually shut that station down, my GF told me they shut the place down and corded it all off. I should have submitted a claim, could have at least got some compensation. The one shop I get inspections at actually mentioned they had a rash of folks with filter & pump service calls.

Now I only go to stations that are certified as 'Top Tier' providers, you can look them up here:

https://www.toptiergas.com/gasoline-brands/

Strongly suggest not buying gas at places not listed. They have inspection standard and test ground tank fuel quality/contamination on regular basis, and will force a station to correct issues or they won't fill the tanks.

As another suggestion, if you see a tanker filling a station, go somewhere else, and wait a couple days before you go back. Filling kicks all kinds of crap up in the tanks and you don't want to run that chit.

Live and learn.


.

[Shiny]

Originally Posted by Schurkey

....
It's entirely possible for them to not seal completely. Even slight leakage of an inlet and outlet will drain everything from the needle valve to the level of the fuel in the tank, given enough time.

Good point. I have never torn a pump apart but every online drawing I find suggests the valves are simple - like a disc or flap that may not have a backing spring to hold it closed. If this is the case, and since there is no significant back-pressure or residual pressure other than the weight of the fuel, I can see how these valves could leak a little.

I think these valves are primarily designed to seal against the internal pressure as the diaphragm moves so maybe not reliable for preventing slow drain-back? They don't have to seal very well to allow the diaphragm to push fuel through the outlet.

So how to know how much they leak?

Would be interesting to know the "specs" on reverse flow rate for these valves.

If, for example, there were 3 oz of fuel in the bowl and line, then a leak would have to be 3 oz/24 hr to drain it in a day. This is over 3.5 cc/hr, which I guess is feasible but sounds like a lot....maybe not?

A 1/2cc/hr leak would drain 3 oz in about a week. That sounds feasible to me, but just guessing.....

Originally Posted by Schurkey

... Thus my suggestion to connect a vacuum pump to the inlet of the fuel pump, to see if--or how badly--the inlet check valves leak.

A vacuum pump might apply enough differential pressure to close a valve that leaks a little under just the weight of fuel above. IMO, this could fail to detect a small leak but if the outlet check valve leaked a lot, this would detect it.

Mike

[Kenth]

Originally Posted by Shiny

IIRC, the stock filter at the carb inlet also has a check valve, correct?Mike

The fuel filter check valve used from 1975, as an vehicle accident rollover security valve so fuel could not escape from fuel tank thru the carb onto the ground, has NOTHING to do with drainback from carb TO fuel tank.

This is described in the 1975 Pontiac Service Manual.

FWIW

[Kenth]

Originally Posted by Schurkey

Even slight leakage of an inlet and outlet will drain everything from the needle valve to the level of the fuel in the tank, given enough time.

This assumes that the inlet valve in the carburetor is at the bottom. I haven't seen any carburetors like that in the 40 that I have serviced carburetors.

[grivera]

Originally Posted by Shiny

Good point. I have never torn a pump apart but every online drawing I find suggests the valves are simple - like a disc or flap that may not have a backing spring to hold it closed. If this is the case, and since there is no significant back-pressure or residual pressure other than the weight of the fuel, I can see how these valves could leak a little.

Mike

The Carter 6907 has springs for the fuel inlet/outlet valves. The rebuild kit included new springs, pins, diaphragm, and sealing discs.

[Shiny]

Originally Posted by grivera

The Carter 6907 has springs for the fuel inlet/outlet valves. The rebuild kit included new springs, pins, diaphragm, and sealing discs.

Just a guess, but seems unlikely to leak a lot. Maybe others are different?

[carbking]

QUOTE "Regardless, I think I've asked before but what specific electric pumps are used for this? I suspect I will want one.

Mike"

END QUOTE

Mike - we were distributors for Carter for years prior to and a few years after their sale to Federal Mogul. Naturally, we looked at Carter products first. I used both the Carter race pump P4594 (7 psi) and P4070 (5 psi) on my own personal performance street vehicles. The P4594 was probably overkill, but I have never experienced any problems with either. I did install the high-buoyancy floats in my dual AFB non-Pontiac set-up using the P4594.

I have the P4070 on my 1974 GTO 350 with the 850 CFM TQ.

Jon

[Shiny]

Thanks Jon

My only purpose would be to fill the carb before trying to start.

I wouldn't need high flow, just a primer, so a "rotary vane" pump like the 4070 feels like overkill.

Is there a simpler, less expensive solenoid pump that would work as a primer and push through the mechanical pump or will a rotary vane pump play better with the mechanical pump?

Mike

[carbking]

Mike - don't know, as stated above, these are the two we always used.

Jon

[HWYSTR455]

Thermoquads are underrated IMO.

I ran a P4594 for years in the 80s with a dual-quad setup .060 over 455 square build. A little loud for my taste but never a hiccup.

.

[chrisp]

Originally Posted by grivera

The Carter 6907 has springs for the fuel inlet/outlet valves. The rebuild kit included new springs, pins, diaphragm, and sealing discs.

Have a 6907 & rebuild kit sealed if any in need.

[Kenth]

Originally Posted by Shiny

Thanks Jon

My only purpose would be to fill the carb before trying to start.

I wouldn't need high flow, just a primer, so a "rotary vane" pump like the 4070 feels like overkill.

Is there a simpler, less expensive solenoid pump that would work as a primer and push through the mechanical pump or will a rotary vane pump play better with the mechanical pump?

Mike

You may look into these. The "Cube" would be a nice primer pump.

https://facet-purolator.com/

I´m using the "Gold-Flow" now after my P4070 got tired after 30+ usage.

[Shiny]

Thanks, Kenth

I'll take a look. It appears in line with my thinking.

[Formulajones]

Okay here ya go. Just to show fuel does not evaporate in a 1/2 hour or even a couple hours.

The first shot is sitting after 2 hours and 15 minutes. I then came back and took a third shot another 2 hours and 31 minutes later.

So this jar sat for a total of 4 hours and 46 minutes.

As you can clearly see the fuel simply does simply evaporate into thin air. At the most that fuel has only dropped 1 /32 of an inch after almost 5 hours of sitting in a very dry climate (7% humidity right now)

So all this talk about fuel just evaporating after sitting a half hour (or even an entire day) simply is not the case. You guys either have a leak somewhere, or you're applying an immense amount of heat to the carb and it's boiling the fuel away.

[Kenth]

Are you comparing a jar with fuel on a bench with much less fuel in a carb sitting on a hot engine that gets hotter 20 minutes after shut off?

[tjs72lemans]

That's a pretty big difference in comparisons. I side with Kenth on the questionable thought.

[Formulajones]

Exactly that's the whole point. You guys have something else going on. It's not the fuels fault. It doesn't just disappear in thin air unless you're excessively heating it or leaking or?????

A different issue needs to be addressed.

There is a reason why multiple cars of mine don't have the problems described here and I don't need a pusher pump