[nUcLeArEnVoY]

My '79 T/A with the factory carb does the same thing that most of the people in the thread are reporting. Starts just about immediately if I crank it up within 14 or so hours of the last start, but if it sits for a day or more, It'll crank for 3-6 seconds after one pump press on the gas pedal before starting up.

I always assumed it was a probably loss of cranking compression because of my aftermarket cam, but apparently this is a very common thing with QJets even when they were new because of their shallow fuel bowls. Lars Grimswud is a QJet disciple over in the Corvette space and he remembers when these cars were for sale and brand new, any cars that were sitting on dealer lots for days on end wouldn't start until after several seconds or more of cranking.

But then you see videos of people starting QJet cars cold at literally the flick of a key. I dunno what to think.

The OP's issue does sound odd, though. Maybe invest in a return line? The check valve in the fuel filters were originally meant to prevent fuel drain back into the rest of the system in the event of a rollover crash, but they also help retain some of the fuel in the carb for starting. Do you also have a thick insulating gasket to also help with preventing fuel from boiling in the carb?

Gas these days in general, even the non-ethanol gas is formulated different from the gas of yesteryear. It's a lot more volatile across the board, and evaporates more readily. It doesn't take much evaporation in combination with the QJets shallow fuel bowl design to compromise the fuel needed for an immediate cold start.

[grivera]

Originally Posted by nUcLeArEnVoY

Do you also have a thick insulating gasket to also help with preventing fuel from boiling in the carb?

.

I do - it's nearly 1/4" thick

Originally Posted by HWYSTR455

Do a pump test into a bucket and time it, might be a pump issue.

Or maybe a fuel sock, or crap in the tank.


.

Good idea for the pump test - the pick up assembly is new and the tank appeared surprisingly clean inside

Originally Posted by HWYSTR455

General replacement tanks for that car are only like $175.



.

Eventually I will install the EFI tank I bought from you - but need to resolve this issue to buy myself time

[SRR]

Are you positive your gas cap is venting?

[grivera]

Originally Posted by SRR

Are you positive your gas cap is venting?

I suppose not - but it is new from Ames and once the car is started it runs well and will start up well within the hour.

[DANTIP]

I've had this problem before and assumed that the only way this could be happening was for the fuel to be evaporating out of the float bowl. I'm not an expert, but fuel fills the float bowl from above and can't "drain-back".

If evaporation is the problem, is there a way to reduce it?

[Kenth]

Originally Posted by SRR

Are you positive your gas cap is venting?

LeMans gas caps are supposed to be closed and venting thru a vent line from the filler tube.

[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.
It was always the case then and more so now with todays fuels aimed for closed fuel systems and fuel injection engines.

FWIW

[DANTIP]

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.
It was always the case then and more so now with todays fuels aimed for closed fuel systems and fuel injection engines.

FWIW

So, when enough fuel evaporates or leaks from the float bowl, the needle valves open and some fuel may come in until the fuel pressure goes down. Then it seems like fuel would continue to evaporate potentially all the way to the fuel pump??

Then when we go to start the engine, fuel has to fill the fuel line and the float bowl(s) before the engine can start? I’m not sure how cars with the return line would act differently? Are there other considerations I’m missing?

[Formulabruce]

Alcohol in fuel makes this problem more pronounced.

[Radman]

I ended up putting an electric fuel pump just in front of the gas tank on both of my Pontiac's. Quadrajet on one Tri-Power on the other. Turn the ignition on, wait for the change in sound from the pump. Pump the gas to set the choke, and they start right away. It is either that or buy race gas.

[intense]

https://youtu.be/7-1Mud8DblA?si=7pjV7INa6rGFIzfU

[Formulajones]

Is there really a need for a car to start fast? Define a slow start.

Cranking for 3-5 seconds after it's sat for a week does not sound unacceptable to me. Certainly not excessive by any means. In fact that's pretty normal. I think people have gotten spoiled with EFI

Now if you're sitting for just an hour and your cranking for several seconds then you likely have an issue to address and a reason for question. Putting a pump at the back of the car is just a bandaid for the root cause. It'll mask the problem but it's not "fixing" it.

It's likely draining out of the carb somehow, or you have an excessive heat problem. There is no way what so ever all the fuel in the float bowl will just evaporated into the atmosphere on its own in just an hour. Not gonna happen.
Now if it's hotter than it should be percolating or something then I'd dive into that area.
The fuel in the float bowl is leaving some other way.

Think about it this way. You can have dry lines, a mechanical fuel pump that's dry or bled off. None of that matters if there is fuel in the float bowl. The engine will start and run with just fuel in the bowl and actually idle for a good 30 seconds or more. It doesn't even need fuel pressure. That's more than enough time for the pump to grab fuel and fill things up.

[Kenth]

Originally Posted by intense

https://youtu.be/7-1Mud8DblA?si=7pjV7INa6rGFIzfU

I wouldn't listen to that guy if I wanted to learn anything!

For example, anyone who has worked with a Holley knows that the needle valves are at the top of the float housings and that a Holley has countless places where fuel can leak.
In addition, all mechanical fuel pumps have a check valve that prevents fuel from "flowing back into the tank".

FWIW

[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.

Instead of guessing, test. After the engine starts and you know there is fuel in the carburetor, fill the carburetor through the bowl vent until it runs out, measuring the amount of fuel added. Let the engine sit for 24 hours after being turned off when hot, and repeat the test. Compare the amounts of fuel.

The twin 4-barrels on my shop truck will be bone-dry after 30 MINUTES! Since they are AFB's there is no way for them to leak down, the fuel evaporates! With a conventional fuel pump, had to crank sufficiently long to fill 4 fuel bowls; seemingly forever.

One other item to consider, is that if the bowl(s) have evaporated dry; the accelerator pump may NOT function on the first stroke even after filling the carburetor bowl, as the accelerator pump well is dry!

Jon

[grivera]

Originally Posted by Kenth

LeMans gas caps are supposed to be closed and venting thru a vent line from the filler tube.

This is how my line is connected - from filler neck to fitting- no line on the other nipple and no idea wher it would lead to/connect

[bhill86]

This is probably worth little to sold the OP’s problem but for discussions sake, after having a similar circumstance I ended up tapping and plugging the well plugs which seemed to improve but not solve my issue. I also made adjustments to the choke and ultimately came to the conclusion that there must be some evaporation.

With less than a few days sitting I get very fast startups after one accelerator press. More than that or all the way to sitting over the off season for a few months I usually crank for 2-3 seconds to bring fuel to the bowl, then press the accelerator once to set the choke and squirt in a pump shot followed by another 2-3 seconds of cranking before it fires.

[Kenth]

Originally Posted by grivera

This is how my line is connected - from filler neck to fitting- no line on the other nipple and no idea wher it would lead to/connect

Here is a pic from the 1969 Service Manual:

[Shiny]

Originally Posted by grivera

This is how my line is connected - from filler neck to fitting- no line on the other nipple and no idea wher it would lead to/connect

Originally Posted by Kenth

Here is a pic from the 1969 Service Manual:

Similar design on my 70 LeMans.

grivera has the U-shaped pipe in place and the diagrams show nothing connected to the open end of the pipe, like his. Assuming the grommet is out of place intentionally, that's the vent design and it should work as intended.

Why they used the u-shape pipe, I don't know. Probably something to do with managing liquid gas... maybe regulatory? Seems weird because, at least on mine, the tank has another vent on the front side that is basically a vertical tube. It has a filter stuffed in it, but no u-shaped turn. ????

Mike

[grivera]

Mine has that vent at front of tank too- I bought/installed the hose with the foam on end of it from Ames

[Shiny]

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

My 70 does, even though it is basically a trickle - more of a controlled vent back to the tank than actually moving fuel to reduce load on the pump.

The tank connections are kind of busy, at least on my 70.

Here's a 70 drawing that might help and some pictures of the U-tube I snagged when replacing the tank.