Carb makes a fountain

[autofahrer]

Carb (Carter avs) was not in use for 20years.
Have changed all seals and everything looked fine.
Bolted on the carb makes a fountain 1m vertical.
Why is there overpressure?
What did i miss to clean or fix?

[taximan]

You forgot to buy an Edelbrock and bypass all this!
Shaun.

[autofahrer]

625?
650?
Can you recomend one?

[NickK]

Hi I have a edelbrock 1406 which you can buy with a Chrysler kickdown throttle adaptor to use the existing linkages and the thing works brilliantly. The 1406 is a 600 with auto choke. My car had a 600 holley vac secondary,before which is late 1971 spec with the manifold operated choke rod which was hard to set up previously.
Cheers Nick

[Richard Calver]

The original fuel system was designed to run at about 2.5 psi and your old AVS was designed to take that pressure. If a modern fuel pump has been substituted, it will probably run about 5 or 6 psi (so called high volume pump). I have had this same problem, not quite a fountain but with a lot of extra fuel flooding the carb. My solution for a while was to fit a pressure limiter and set it as low as possible. Then I did what is suggested and bought an Edelbrock 1406. This is a copy of the AFB which was used on our cars before the AVS came in. You can get an Edelbrock copy of the AVS if you wish - it is in their Thunder series. But for a 383 you would want about 600 cfm rating and I think from memory the Thunder series were higher than that. The 1406 is perfect in this application.

[taximan]

You also get the option of an electric choke, the 1406 is set lean for economy, but if you tune your engine a little in the future, kits are available to change it all without having to take the carb apart.
Your original carb will have invisible wear that just isn't worth getting into (unless your name is Barnett)
Do a thorough search for a decent price, there's always someone with a special offer.(USA)
Shaun.

[Chris_R]

625?
650?
Can you recomend one?

CFM is calculate by:
SCFM (100% Volumetric Efficiency) = Displacement (ci) x RPM / 3456

Displacement = 440
RPM (max say 5,000)

SCFM = 440 * 5000 / 3456

SCFM (Sea level cubic feet per minute) = 636.

You probably have at best 90% to 95% VE, so at best your engine will consume between 575cfm and just over 600CFM (at 5,000rpm).

[autofahrer]

thanks for the math lesson,
why do so many mopar-ethusiasts recomend the 650 edelbrock?
my local v8-guy gave me a math lesson with result: 625 (witch is carter avs 1944) is to small for the 383 engine...

[Chris_R]

An old thread, but the question has long puzzled me as to exactly why it was always recommended to install a larger cfm rated carburetor than the maths indicate that the engine needs and I think I have the answer.
Carburetor flow ratings (in cfm, or cubic feet/minute) are taken at an arbitrary vacuum drop of 3.0-inches Hg for two-barrels (50.8mbars) and 1.5-inches Hg (101.6mbars) for four-barrels and there is no guarantee that, at maximum rpm with a wide open throttle, any given engine will actually see the theoretical vacuum drop for which the carburetor is rated. If there is a lower than expected vacuum drop then the carburetor will become a restriction. A higher cfm rated carburetor allows a lower vacuum drop to still supply the engine with the maximum it needs. It is also to do with Volumetric Efficiency which is a measure of the efficiency of the induction process and the air filter, carburetor, intake manifold, intake port, intake valve all affect the amount of air which an engine of given displacement volume can take in.
Most write-ups that I have seen suggest increasing the engine cfm requirement by between 1.1 and 1.3 for a single plane inlet manifold and by between 1.2 and 1.5 for a dual plane inlet manifold as a broad approximation for general use.