Carburetor Questions

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Mar 11, 2007 | 06:31 PM

project40

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Joined: Sep 2006

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From: Grantville, PA

Carburetor Questions

I'm trying to identify and diagnose the carb on my new (to me) truck. I looked over it and it is a Holly 4 barrel and I think it is a part number 4777. The only numbers I could see on it was that 4777 at a couple places, 2826 and 6R3760. It leaks fuel from the bottom of the rear bowl after I shut the truck off. The truck diesels and finally stops. I put a clamp on the fuel line for now but I'm trying to figure out what to do. I'm thinking I need to rebuild the carb but I may try adjusting the fuel level first to see if that helps. Any thoughts or advice?

Mar 11, 2007 | 10:09 PM

airharley

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From: Escondido, CA

http://www.holley.com/data/TechServi...%20Listing.pdf
You can find the list # on the choke horn, housing that sticks up where the choke plate is. From there you can find all the info on the link above. Most likely you have something stuck in the needle and seat. You can pull it out to check then reinstall it. Most likely the reason for desieling is the over flow of fuel into the engine from the vent tube. Check out the rest of the holley website for info on how to set your bowl floats and so on. Hopefully this gets you pointed in the right direction.

Mar 12, 2007 | 09:12 AM

jowilker

Fleet Owner

Joined: Jun 1999

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From: Creedmoor, North Carolina

To add to Mark's comment, timing too high and idle too fast can contribute to the dieseling as well.

John

Mar 12, 2007 | 08:01 PM

66F100Again

Tuned

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From: Massachusetts

If the needle and seat are clean and working, check the float. Maybe a pin-hole or something and it's letting too much fuel in from the fuel pump residual pressure after you shut off the engine.

Mar 13, 2007 | 01:12 PM

Jfollender

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Joined: Dec 2006

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I had a similiar problem. Has the truck been sitting? If so, you may have bad gas, which may prevent the needle from "seat"ing and overload your bowl.

Mar 13, 2007 | 01:28 PM

LxMan1

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From: Louisville,Ky.

The carb is a 650cfm Dual line/double pumper carb.
Sounds like the rear float is too high. Remove the sight plug on the side of the bowl and adjust it down until the fuel level is just below the sight hole. This will leave plenty of fuel in the bowl for those WOT runs, but a low enough level for the fuel to expand when it heats up. If it won't adjust down, then there is probably a small piece of debris in the needle and seat, Remove it, clean it out then readjust the float. Also make sure that there is an inline fuel filter between the pump and carb. Holleys do not like any crud in them.

Mar 13, 2007 | 05:58 PM

project40

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Joined: Sep 2006

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From: Grantville, PA

Thanks for the help guys I pulled the rear bowl off tonight to inspect it. The gaskets are all dried out and brittle, the diaphragm is cracking apart. The inside of the bowl is really varnished. I guess I'll get a new gasket and diaphragm and reinstall after I clean it out. Then when I get my radiator repaired or replaced I can set the float level.