1975 390 2 barrel carb

Engine, ignition, fuel, cooling, exhaust
andypayne86
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1975 390 2 barrel carb

Postby andypayne86 » Sun Dec 18, 2016 8:22 pm

I have a 1975 390 our of a truck in my 64 galaxie. It is drinking gas like, I don't know what. It will use a quart of fuel in minutes idaling. You can literally watch the fuel leave my can. (It has a gas can hooked up now. I am restoring it. Have a new tank was waiting to put it in till I fix the trunk pan) FuEl system is new, everthing, the carb is a factory 2 barrel( big butterflies) that has been dipped and rebuilt. I adjusted the carb using my vac guage, till I reached max vacuum. At this rate I could not make it to a gas station from the house. I have it in the shop I know it is not leaking fuel nor is it mixing any where, does not smoke, not running out the pipes. Any thoughts???

cep62
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Re: 1975 390 2 barrel carb

Postby cep62 » Tue Dec 20, 2016 7:51 pm

:wel:
Welcome to the site .

I use a small can to run an old engine when I don't trust the stock tank.
A quart or two of gas doesn't last long idling . take it out and run it.

Although old big engines don't get the millage as the new small stuff does, but you look cooler at the gas station.

markguiver
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Re: 1975 390 2 barrel carb

Postby markguiver » Fri Feb 17, 2017 8:25 am

The stock mechanical pumps are rated at 25-30 GPH. At full flow that equates to 1/2 gallon per minute. Even if it's only half that when idling a quart would only last 60 seconds. The usage you posted sounds about right to me. You know what they say; our old trucks pass everything but a gas station.
Mark.

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dillon2
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Re: 1975 390 2 barrel carb

Postby dillon2 » Sat Feb 18, 2017 6:30 am

markguiver wrote:The stock mechanical pumps are rated at 25-30 GPH. At full flow that equates to 1/2 gallon per minute. Even if it's only half that when idling a quart would only last 60 seconds. The usage you posted sounds about right to me. You know what they say; our old trucks pass everything but a gas station.
Mark.

Aint that the truth. My 73 F250 trailer special gets 10 mpg all day long.....loaded or empty. :-D

BIGJOE1979F250
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Re: 1975 390 2 barrel carb

Postby BIGJOE1979F250 » Sat Apr 22, 2017 12:45 am

I know that if you had a Four barrel carb on it , it would be more gas efficient. That is as long as you don't "step it down" and get those other two barrels engaged. But you would also most likely have to put 4bbl heads and manifold on it too. I have had "63 to "66 Mercurys that taught me that lesson. While you can get an adapter plate that converts your 4bbl manifold to accept a 2bbl carb, i don't think that there's a conversion the opposite way. The difference is in the size and placement of the holes in the heads and manifold. Hope this helps.


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