Why Won't My Carburetor Suck?

[Eagle43]

I have a 52 F1 with an 8BA V8. For some reason I can't get any vacuum from the vacuum port on the Holley 94 so consequently I don't get any spark advance. I have a hard line from the carburetor to the spark advance and checking with a vacuum gauge I get absolutely nothing. I've had the carburetor apart and gave it a thorough cleaning and blown through the port and it's clear. I get about 17 at the intake manifold. Its got me stumped. Any help would be much appreciated.

[38 coupe]

The port is a combination of venturi vacuum and induced vacuum above the throttle plates. The value is small, I doubt your vacuum gauge will read it. In the carburetor make sure the base has the little hole that lines up with the vacuum advance passage in the center section. Also make sure the gasket between the two has a hole that lines up with the passages, and is put on right side up so it lines up with the passages. Finally make sure the vacuum advance diaphragm is ok, and you should be good to go. Verify with a timing light with everything hooked up. You will see advance as you smoothly rev up the engine, no advance at idle.

[Eagle43]

Originally Posted by 38 coupe

The port is a combination of venturi vacuum and induced vacuum above the throttle plates. The value is small, I doubt your vacuum gauge will read it. In the carburetor make sure the base has the little hole that lines up with the vacuum advance passage in the center section. Also make sure the gasket between the two has a hole that lines up with the passages, and is put on right side up so it lines up with the passages. Finally make sure the vacuum advance diaphragm is ok, and you should be good to go. Verify with a timing light with everything hooked up. You will see advance as you smoothly rev up the engine, no advance at idle.

Thanks. This confirms what I discovered last night by putting the middle section under water and blowing air into the port. I didn't realize that the port was connected to two sources of vacuum, one in the middle section and another going down into the base. I mistakenly installed a base from an older 94 because I needed the longer throttle shaft for the hand throttle. I installed the proper base and the longer shaft. Now I get 4 lbs. vacuum on the line and the timing advances as it should. In the attached picture you can see the extra hole (next to the idle mixture screw) in the left base that is missing in the right base.

[tubman]

Thanks for documenting this so well. If this thread doesn't convince people to not mix "Load-A-Matic" and non "Load-A-Matic" components, nothing will.

[Eagle43]

I just took the truck for a quick spin around the neighborhood and all seems to be well.

[Mart]

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Good news! Parts can be mixed and matched but obviously within limits.

[glennpm]

What is the other hole for on the right-hand base?

[Mart]

It's the vacuum port to "suck" the power valve closed. There should be one on the other base too.

[glennpm]

Thanks Mart.