Carb Drain Back
Thread Starter
Racer
Joined: Nov 2019
Posts: 336
Likes: 173
From: Canadian living in southern France
Carb Drain Back
If I leave my poor old '76 alone for a week or so, I can get it to start after the second try and a bit of accelerator pumping. After three weeks, it takes a lot more.
Fine, I installed an anti-drain back valve and it helped --- not at all.
Fine, I bought really good, racing quality anti-drain back valve, and it helped --- more or less. After three weeks, my clear fuel filter is pretty much empty, and yes, the valve is between the carb and the pump.
I've seen this complaint here before.
I had a '75 Cadillac that I stored every winter while I lived in Canada, ( winters were a really long time!), and after five months, it started right away, and it had a Quadrajet, and no anti drain back valve.
What gives??
I'm starting to think electric fuel pump.
All ideas from this excellent site are always welcome.
Fine, I installed an anti-drain back valve and it helped --- not at all.
Fine, I bought really good, racing quality anti-drain back valve, and it helped --- more or less. After three weeks, my clear fuel filter is pretty much empty, and yes, the valve is between the carb and the pump.
I've seen this complaint here before.
I had a '75 Cadillac that I stored every winter while I lived in Canada, ( winters were a really long time!), and after five months, it started right away, and it had a Quadrajet, and no anti drain back valve.
What gives??
I'm starting to think electric fuel pump.
All ideas from this excellent site are always welcome.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,209
Likes: 9,347
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
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I had an Edelbrock onecway valve that didnt work well. Not sure ifvthe fuel in yhe bowl seeped out or evaporated with the heat of yhe engine. It was aleways hot.
Well i switched to EFI at one point which had me install an electric pump circuit..... yada yada yada, Went back to carb and installed a low pressure electric fuel pump. I should have done it years ago. Never one issue but always use s fuel pressure regulator with either style pump.
Well i switched to EFI at one point which had me install an electric pump circuit..... yada yada yada, Went back to carb and installed a low pressure electric fuel pump. I should have done it years ago. Never one issue but always use s fuel pressure regulator with either style pump.
Advanced
Joined: Apr 2020
Posts: 80
Likes: 14
From: Ont, Canada
I don't believe you mentioned what kind of carb this is. I can tell you this though . Today's gas , compared to years ago ( 1970's ) will evaporate much quicker.
It is common for a car with a carb and mechanical fuel pump to require cranking of the engine to refill the fuel bowl after sitting for a couple of weeks. Any carb with undetected fuel leakage will add to this . What carb is it?
The only solution to this is to install an electric pump that will prime/refill the fuel bowls when the key is turned on.
It is common for a car with a carb and mechanical fuel pump to require cranking of the engine to refill the fuel bowl after sitting for a couple of weeks. Any carb with undetected fuel leakage will add to this . What carb is it?
The only solution to this is to install an electric pump that will prime/refill the fuel bowls when the key is turned on.
Race Director
Joined: Nov 2006
Posts: 13,225
Likes: 7,823
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Over the years I had 2 different carbs on my 77. With both I experienced the same thing you do now. Crank, crank, crank. Wait a couple seconds, Crank, crank, crank. Finally fire.
For about 30 years this was just how it was if it sat for a week. which it often did.
EFI about 3 years ago. Electric fuel pump in tank. Turn on key. Crank, fire, back out of the garage.
Done!
For about 30 years this was just how it was if it sat for a week. which it often did.
EFI about 3 years ago. Electric fuel pump in tank. Turn on key. Crank, fire, back out of the garage.
Done!
Team Owner
Joined: Mar 2002
Posts: 44,671
Likes: 1,830
From: Huntsville AL
A 40 something year old Chevy with a carb and mechanical fuel pump is going to require some level of cranking the engine over to refill the fuel bowl after sitting for a few weeks. When it doesn't start I would worry, until that happen just enjoy the ride.
Drifting
Joined: Oct 2020
Posts: 1,567
Likes: 576
From: Wisconsin
Pretty normal behavior, especially with todays gas. Mine, anything less than 24 hrs sitting, and I don’t think the crankshaft turns more than 90 degrees and it’s running. Anything more than 24hrs sitting, and it’s crank for 2-3 seconds, stop, pump the gas 2-3 times and she lights off with gusto. No anti-drainback valves or one way filter or anything.
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Le Mans Master
Joined: May 2008
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2022 C3 of the Year Finalist - Modified
No big deal.....nothing to fix. Its iust the way it is. My 77 has Holley double pumper, NO choke, starts us in 3-5 seconds or less. Doesn't make it wrong, or a reason to go spend thousands of dollars on fuel injection. Same with my Harley, except with choke out it starts almost instantly......choke back in after a few seconds. No big deal, unless you make it a big deal in your head.
Safety Car
Joined: Oct 2007
Posts: 4,378
Likes: 1,740
From: Seattle Area Washington
No need for ANY excessive pumping...
Extended periods of non running crank engine 5-10 seconds, stop.
Press accelerator pedal to floor once and slowly release.
This should close choke plate and set fast idle cam to high step.
Crank engine 1-5 seconds it should fire and build up to 1150-1400 RPMS.
My 77 with Hot Air Choke at 60+-* ambient runtime 3-4 minutes max choke full vertical tap accelerator, drops off fast idle to 550 or so RPMS
Extended periods of non running crank engine 5-10 seconds, stop.
Press accelerator pedal to floor once and slowly release.
This should close choke plate and set fast idle cam to high step.
Crank engine 1-5 seconds it should fire and build up to 1150-1400 RPMS.
My 77 with Hot Air Choke at 60+-* ambient runtime 3-4 minutes max choke full vertical tap accelerator, drops off fast idle to 550 or so RPMS
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
No big deal.....nothing to fix. Its iust the way it is. My 77 has Holley double pumper, NO choke, starts us in 3-5 seconds or less. Doesn't make it wrong, or a reason to go spend thousands of dollars on fuel injection. Same with my Harley, except with choke out it starts almost instantly......choke back in after a few seconds. No big deal, unless you make it a big deal in your head.
A choke does nothing if the bowls are empty, I figure.
I find it stimulating to pump the snot out of these old-style carbs. Right hand turns key. Left hand has fingers crossed.
Pushing a fob button is so boring.
Is my vette stock?? HAHA
Joined: Oct 2015
Posts: 20,209
Likes: 9,347
From: Im not allowed to tell you
2020 C3 of the Year Finalist - Modified
2020 Corvette of the Year Finalist (performance mods)
2019 C3 of Year Winner (performance mods)
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Thats only if you have a choke, some folks down south dont need them. But you will always need to pump if there is no fuel in the bowl for the accelerator pump. Once you have fuel and you get a few squirts you will be all set. Another and better way without pumping would be to use starting fluid. Just give it a squirt and turn the key. It will fire right up and fill the bowl. Should run long enough to staybrunning too.
Thread Starter
Racer
Joined: Nov 2019
Posts: 336
Likes: 173
From: Canadian living in southern France
I don't believe you mentioned what kind of carb this is. I can tell you this though . Today's gas , compared to years ago ( 1970's ) will evaporate much quicker.
It is common for a car with a carb and mechanical fuel pump to require cranking of the engine to refill the fuel bowl after sitting for a couple of weeks. Any carb with undetected fuel leakage will add to this . What carb is it?
The only solution to this is to install an electric pump that will prime/refill the fuel bowls when the key is turned on.
It is common for a car with a carb and mechanical fuel pump to require cranking of the engine to refill the fuel bowl after sitting for a couple of weeks. Any carb with undetected fuel leakage will add to this . What carb is it?
The only solution to this is to install an electric pump that will prime/refill the fuel bowls when the key is turned on.
Race Director
Joined: Mar 2016
Posts: 14,396
Likes: 8,203
From: Napa Valley California
Leave it alone.
It isn't broke.
It's the same as my 73.
If I start it every day, it starts with the first click of the starter.
If I don't drive it for a week or so it takes a few seconds of cranking.
Two weeks or more, I pump the gas, turn the key for several seconds, pump the pedal again, and then it will start.
It's an old chevy design and not fuel injected.
I don't know of any real fix other than EFI.
It isn't broke.
It's the same as my 73.
If I start it every day, it starts with the first click of the starter.
If I don't drive it for a week or so it takes a few seconds of cranking.
Two weeks or more, I pump the gas, turn the key for several seconds, pump the pedal again, and then it will start.
It's an old chevy design and not fuel injected.
I don't know of any real fix other than EFI.
Race Director
Joined: Nov 2006
Posts: 13,225
Likes: 7,823
From: Sunshine Coast, Queensland, Australia
2025 C3 of the Year Finalist - Modified
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Cruise-In VIII Veteran
Yup, And the EFI is great!
Oh and my aging Harley has EFI as well, came that way. Also great!
Oh and my aging Harley has EFI as well, came that way. Also great!