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carburators

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Anonymous-0

Well-known Member
I have a 70 ford truck with 391 cid equiped with an edlebrock four barrel carb. If it stands a few days I have to pour gas in the carb to prime or it wont start. What could be allowing it to lose prime. I did an overhaul kit on the carb but did not do anything with accelerator pump. can that be the problem .thanks.
 
no ,maybe . Before3 you try to start it , look down he carb and open the throttle . do you see fuel spray ? If you do ,pump is working, if not mcrank it over few times ,, then try again ,,fuel spray ? If yes ,you have fuel delivery problem
 
Some carbs will allow fuel to siphon back. Stop by napa and pick up a fuel filter with a check valve in it. It was a common problem.
 
Sounds like a weak fuel pump that won't pump @ cranking speed but will when the engine fires and takes off on the gas you primed the carb with.
 
If this is a take off of the old Carter 4bbl, carb and not a Holley like should be on a 391 with a vac. gov. then there is a crack someplace in the lower body . If it looks like a holley with two float bowls and metering blocks then your problem is a power valve that is draining the float bowl on the accelerator side . Pictures i need pictures . since i can not see what is on it but i know WHAT SHOULD BE ON IT. I am not up on what comes out of the speed shop books anymore .
 
Once you get it started how does it run?
Sounds like you're losing gas out of the float bowls. If it loads up and runs way too rich it's a bad power valve. If it runs ok but sputters on acceleration it's a bad accelerator pump. Could be bad gasket between the float bowl and metering block, needle valve sticking closed, fuel pump with a leaking diaphragm. Need more info.
 
I kept blowing power valves on a 390, a local guy asked if I had two gas tanks and did I run them dry before changing tanks. Yes to both, after that I never let it run completely dry and I never blew another power valve.(high vacuum when you run them dry)
 
It"s not possible to have a power valve problem on an Edelbrock carb, they don"t have power valves. What"s most likely going on is the fuel is being boiled out of the carb. Try sticking a phenolic 1" open spacer under the carb to insulate the carb from the heat of the intake manifold. It might even perform a little better. Several of the guys on the FE forum say dyno testing usually confirms about 10hp with a 1" open spacer and not a 4 hole.
 
Have a edelbrock carb and intake on my small block chevy and it would do basiclly the same thing. I put the phenolic thick gasket between the carb and intake and it made a huge differance. It stopped the heat transfer from the intake to the carb which would boil the gas out of carb. Also like said your fuel pump make be getting a little weak since it wont fill the carb back up at cranking speed. Dave
 

As others have posted it could be a fuel boil issue and you may want to address that. However, I like to run an electric fuel pump which allows the fuel bowl to fill before cranking the engine. I find it reduces cranking time especially for vehicles that are not used every day.
 
the edlebrock on my chevy truck with a 454 does the same thing once started it will fire right up even if it sits a few hours, but overnight the float bowl draines it will start, but you have to crank it a long time, i know gm 4bbls have plugs in the bottom which over time will leak , but i dont know if the edlebrock does, mines about 5 years old
 
Have had this problem on many different carb brands. After changing the fuel pump problem solved. Took a few of the bad fuel pumps apart and found pin holes in the diaphragms that allowed the fuel to be siphoned back to the tank after shut down.

Leonard
 
Bowl in carb should remain full for many day, weeks after shut down. It is either percolating over into manifold when shut down hot or leaking out , either into manifold or to outside. A short burst on the starter, and then wait like 30 seconds before trying again should get enough gasoline into carb to start if fuel pump and filter are any good at all. Need to stick you neck in and take a look after shut down.
 
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