[Shiny]

I decided to add an inline primer pump just to fill an empty carb and avoid cranking for 15 seconds.

My 350 is basically stock with a Quadrajet so I'm not worried about starving it for fuel. The car still has its original 2-bbl 5/16" fuel line. If I had more than about 350hp and ran full throttle, this approach probably would be stupid.

I used a Facet Cube pump (thanks to Kenth for suggesting) that was configured for 7 psi max pressure and "flow-through". I also decided to use the biggest inlet and outlet fittings available, which were 3/8 NPT. Their PN is 40109 and I ordered it from Pegasus who stocks a lot of their pumps: Link to Pump Listing

I wanted to install it with hard lines but without a lift, rubber fuel line had to happen to accommodate the limitations of my elder body.

I mounted it near the fuel pump where the line was accessible and I could install a couple nutserts in the frame. I bought the rubber isolation mount and bent a bracket so I could mount it vertically. I didn't like hanging it sideways suspended by the rubber cushions. People have expressed a preference for mounting a pump near the tank but this one is rated to lift 60" so I'm optimistic it can generate enough suction to fill the carb. Hopefully the electric pump can push fuel through the mechanical pump.

I bought a fuel pump installation harness with a bigger relay than I need and installed a momentary switch wired to the accessory terminal on the fuse box. This way, it will only run when the key is in the ignition and a finger is on the switch.

It took me about 5 times longer than I expected and a lot more work and part scrounging than I want to admit.

Will it be worth it? I don't know yet. I will have to run it a few times to see how it works and gain confidence.

Basically, fingers crossed. I still need to strain-relieve the wires but so far, it acts like it's pumping gas.

[Schurkey]

Originally Posted by grivera

My 69 Lemans has a factory metal fuel line with no return. New rubber lines

HOW MUCH "rubber lines"? The manufacturer uses the minimum amount of rubber, with non-porous steel or hard-plastic tubing for most of the plumbing.

Rubber fuel hoses are porous. Fuel vapor escapes through the rubber, leaving no traces except the smell of fuel if the vehicle is in an enclosure (reasonably well-sealed garage.) Thus the popularity of hose with Teflon- (PTFE-) liner. And even that should be minimized.

Originally Posted by grivera

extended cranking doesn’t help.

Which indicates that even the fuel pump has gone dry. Or it's defective, or the fuel pump eccentric is defective.

Originally Posted by PontiacHO

What temperature does your engine typically run? Could be fuel percolating in the fuel lines.

Less a matter of engine coolant temperature, and more a matter of intake manifold temperature--for example, overheated due to excessive exhaust flow through the exhaust crossover in the intake manifold causing fuel percolation in the floatbowl.

Originally Posted by Verdoro 68

I read most mechanical fuel pumps already have anti-drainback valves by design.

Yup. Couldn't function without them.

Originally Posted by Verdoro 68

The fuel pump in my car is at least 10-12 years old so I'm going to try two things - a fuel filter with an anti drainback valve and a fresh fuel pump.

TEST your pump before replacing. New fuel pump quality is very questionable. If your pump is functional, you're probably better-off with it than with a new one.

Originally Posted by grivera

Does not having a return line to the tank affect this at all? It’s as designed by PMD.

Perhaps. The OEM vapor-return was intended to reduce fuel pump vapor lock by providing a simple, easy way to vent vapor back to the tank. There's a restriction--perhaps .030--.060 that vapor can pass easily, but which restricts liquid fuel flow.

Originally Posted by grivera

the fuel pump rebuilt with an American made kit from a reputable recommend company.

Check-valves replaced? Tested afterwards?

Originally Posted by Kenth

I have found fuel "drain-back" thru fuel inlet is a myth.

If the float level drops enough to open the needle valve, AND the fuel pump check valves leak, sooner or later the fuel from the fuel tubing will drain back to the level of the fuel in the tank. So how far it drains back depends somewhat on how full the tank is--and if the vehicle is parked on an incline.

Once the fuel pump gets airlocked, it'll take extra time--more cranking--for it to re-prime. An in-carb fuel filter with the check-valve can reduce or prevent the whole fuel plumbing including the engine-driven fuel pump from siphoning back to the tank.

Originally Posted by Kenth

Fuel evaporation is not, as the carb is 100% vented to atmosphere.
It was always the case then and more so now with todays fuels aimed for closed fuel systems and fuel injection engines.

Yeah, they're not so picky about Reed Vapor Pressure any more. It's not like they ignore it...but I bet the standards have slipped.

[tanksteve]

I went through this issue with several different cars with q-jet. The fuel bowl would go dry in 3 days every time. Each time removed the carb and checked for leaks out the central bowl, there were none. Replaced the q-jets with Holleys and the fuel bowls would still have fuel a month later and the cars would start right up. I considered adding a booster electric fuel pump as some here have suggested and that would have fixed the problem also.

[grivera]

Originally Posted by Schurkey

HOW MUCH "rubber lines"? Rubber fuel hoses are porous. Fuel vapor escapes through the rubber, leaving no traces except the smell of fuel if the vehicle is in an enclosure (reasonably well-sealed garage.) Thus the popularity of hose with Teflon- (PTFE-) liner. And even that should be minimized.

Which indicates that even the fuel pump has gone dry. Or it's defective, or the fuel pump eccentric is defective.


Perhaps. The OEM vapor-return was intended to reduce fuel pump vapor lock by providing a simple, easy way to vent vapor back to the tank. There's a restriction--perhaps .030--.060 that vapor can pass easily, but which restricts liquid fuel flow.


Check-valves replaced? Tested afterwards?

The car retains the factory metal supply line. I replaced the short piece of rubber line at the tank and the short piece that supplies the pump.

The eccentric is intact and operates the pump fine after the car starts. And the car will start within an hour. Maybe the metal fuel line has pinholes(s) in it making it hard to get prime? Thing is, I don't smell any fuel and no wet spots.

The Carter pump was fully rebuilt, new check valves and tested per the Carter rebuild video.

[Kenth]

Originally Posted by Schurkey

If the float level drops enough to open the needle valve, AND the fuel pump check valves leak, sooner or later the fuel from the fuel tubing will drain back to the level of the fuel in the tank. So how far it drains back depends somewhat on how full the tank is--and if the vehicle is parked on an incline.

If this would be true, the inlet valves would be located at bottom of the float bowl. Truth is that in all carbs Pontiac used for the V8´s has the fuel inlet valve located in the airhorn, above the float, 2G´s 4G´s and AFB´s, except the Quadrajet, the Quadrajet has the fuel inlet valve located on an elevated location in the float bowl, and cannot drain completly if the check valve in fuel pump is broke.
Anyhow, Rochester made the fuel bowls small in the Quadrajet so the loss of fuel would be minor, due to evoparation.
And, the 1975 and later carb fuel filter check valve was a part of GM´s accident roll over policy, for fuel to not drain thru the carb if the vehicle landed on the roof at an accident.

FWIW

[Shiny]

I don't buy into significant loss through the fuel hose.

Mine had a short piece at the pump and another at the tank. Call it 2 feet total.

I find J30R9 is spec'd and/or ceritified to have max permeability of 15 g/m^2/day at 40C (105F). Do the math for 3/8" hose and it might add up to 0.6 ml per day for that 2 foot section. At 70F, the loss will be a lot less, maybe 0.2 ml per day.

Shutting down from warmed up, my carb would lose enough gas to not start in about 3 days. To me, this means at least 2 ounces (60 ml) are going somewhere. Let's say 60 ml/ 5 days to be conservative, or 12 ml/day.

1 ml loss through the hose in those 5 days might contribute a little, but not enough to matter IMO.

I'm still banking on evaporation as the dominant mechanism.

And I hope my primer pump works because I don't like cranking for 15 seconds.

It is definitely possible my pump is allowing some leakage, but as Kenth explains, it can't all go down the line.

Since my pump is a short can version, more typical for 2 bbl carbs, maybe a tall can pump will fill the carb quicker? Could this explain why others don't crank as much to refill their carbs?

Mike

[Schurkey]

Originally Posted by Kenth

If this would be true, the inlet valves would be located at bottom of the float bowl.

I'm not saying that leaky checkvalves in the fuel pump will drain the float bowl.

I'm saying that once enough fuel evaporates/leaks in the float bowl to drop the float, and open the needle valve, leaky check valves in the fuel pump allow everything from the needle valve down to the level of fuel in the fuel tank, to drain backwards. Air enters at the needle valve, and the plumbing drains down to the level of the gas tank, with the time required being dependent on how badly the check-valves in the pump leak. Adding a check-valve in the filter at the carb would prevent the back-flow of air into the plumbing, greatly reducing or eliminating the siphon-effect draining the tubing and perhaps the fuel pump.

If that allows air into the fuel pump itself, the pump is now vapor-locked and will have some trouble re-priming. Thus the "vapor return" plumbing on cars with A/C, and some others where the engine compartment is known to be particularly hot.

Even if the fuel pump doesn't get air in it, not only does it have to re-fill the float bowl, it also has to re-fill all the fuel plumbing on the pressure side of the pump that emptied-out.

Originally Posted by Shiny

I don't buy into significant loss through the fuel hose.

Mine had a short piece at the pump and another at the tank. Call it 2 feet total.

I find J30R9 is spec'd and/or ceritified to have max permeability of 15 g/m^2/day at 40C (105F). Do the math for 3/8" hose and it might add up to 0.6 ml per day for that 2 foot section. At 70F, the loss will be a lot less, maybe 0.2 ml per day.

My concern was that the original poster had rubber from front to back. I've seen guys do this because "it's too much hassle to route metal tubing through the frame."

[Shiny]

Working so far and I'm happy enough for now.

Pumped pedal twice, cranked, nothing.

Ran the electric primer until it stopped buzzing.

Pumped pedal twice, cranked, fired like it should.

Fingers crossed it keeps doing this.

[Shiny]

Originally Posted by Schurkey

....My concern was that the original poster had rubber from front to back. I've seen guys do this because "it's too much hassle to route metal tubing through the frame."

I resemble that!

It would indeed be a hassle running metal the full length without a lift.

Maybe if I was 20.

I'm not so I accept my limitations and ran hose from the electric pump behind the front wheel well to the mechanical pump.

[Shiny]

Originally Posted by Shiny

Working so far and I'm happy enough for now.

Pumped pedal twice, cranked, nothing.

Ran the electric primer until it stopped buzzing.

Pumped pedal twice, cranked, fired like it should.

Fingers crossed it keeps doing this.

Son came up for father's day. Car had been sitting for a couple months since last started so gave me a chance to check out the primer pump.

As you can hear in the video, it took about 15 seconds of electric pump operation to fill the bowl, then I hit the gas pedal to set the choke and get the accelerator pump in the carb squirting. It took only 3 short starter bursts to fire off, which is a HUGE improvement over waiting for the mechanical pump to fill the carb.

Good enough!

Link to Video of Cold Start Using Primer Pump