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Old 10-11-2006, 10:32 PM
oldfomoco oldfomoco is offline
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Question proper carb for a 72 F-250 w/390, 4spd 2wd

I am considering buying a 72 Ford F-250 2WD w/390, 4spd. It seems to run okay, but runs REAL RICH. Lopey idle, will stall if u dont feather the accelerator pedal, real black smoke out of the dual exhausts. Has headers and a 600 cfm 4 barrel holley on it now, owner says it's been rebuilt, I don't think so. Any suggestions as to which 4 barrel carb would work the best for mileage and performance? Thanks.
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Old 10-12-2006, 12:08 AM
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Edlebrock seems to have a good economic and low maintenance carb. Check out Summit Auto Racing. If you're in Northern Nevada, I know there is a Summit Outlet in Sparks. The folks at Summit are pretty knowledgeable about which CFM, Jet Size, etc, and will set you up with the right stuff.

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Old 10-12-2006, 04:30 PM
oldfomoco oldfomoco is offline
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Thanks, I appreciate the input. I don't know why I didn't think of Summit!! I've bought from them before for an 88 Stang GT I used to have. DUH!! Old age creeping up on me I guess!! Thanks again!!
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Old 10-19-2006, 05:59 PM
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Holly makes a good carb - you just have to dial it in for your application. Their website has directions and examples. I would sure try this before I bought a new one!
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Old 11-01-2006, 08:14 PM
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Best Carb for a 390

Quote:
Originally Posted by oldfomoco
I am considering buying a 72 Ford F-250 2WD w/390, 4spd. It seems to run okay, but runs REAL RICH. Lopey idle, will stall if u dont feather the accelerator pedal, real black smoke out of the dual exhausts. Has headers and a 600 cfm 4 barrel holley on it now, owner says it's been rebuilt, I don't think so. Any suggestions as to which 4 barrel carb would work the best for mileage and performance? Thanks.
Usually when it won't hardly idle, there is a problems with high float level, or a needle and seat which is leaking, or a plastic float which is leaking. It is super easy to replace the needle and seat in a Holley, it is all external. If the float is bad, adjusting the float level with the sight screw removed will fail, as it would with a bad needle and seat. Replace the needle and seat and adjust for float level. If you can't, then the float is bad. Another thing to check is a ruptured power valve. A backfire can rupture the diaphragm and cause fuel to dump in but not at idle. Get a book on a Holley, so you understand what you are doing. What I call the sight screw is on the side of the float bowl for the correct float level, and it is intended to allow you to adjust float levels with the engine running.

To learn the carburetors stock size jetting, you need its List Number which is on the primary side facing forward. take the air cleaner off and you will find it. You can go to the Holley web site and get all the stock sizes for your carburetor. The Holley, IMO, is by far the best carburetor for both performance and mileage. Problems like yours are common, and can be easily fixed.

Willy B is absolutely correct. And the 600 CFM is perfect for the 390. Unless the 390 was a high rpm built up motor, it does not need more, and the smaller size is far better for low speeds, and you will have better flow through the smaller venturis.

I have used Carter AFBs before (which is what the Edelbrock is) and they are rather finicky and require tons of parts sets to get the jetting corect.(Edelbrock is very good about proper jetting on a special order) When you live at altitude, you are wanting to lean out the stock jetting and that is where the problem begins. They use "step rods" for power enrichment and final jet size. The step rods eventually wear the jet and cause enrichment. Any increase or decrease in jet size affects the power jetting, so increases or decreases must be done with both step rods and jets. You also have to remove the entire carburetor top to work on this. The Holley, in contrast, is far easier to work on, and unless the base and center part are warped, the thing will last forever.

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Alanco
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Last edited by alanco; 11-01-2006 at 08:18 PM. Reason: addition
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Old 11-01-2006, 08:14 PM
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