Vacuum Line

[Ray C.]

I have had to replace my 250HP 1965 intake manifold and carburetor with the correct units. The Holley that was installed did not have a vacuum line running from the rear of the carburetor on the right side down along the exhaust manifold. (Parallel to the thermostat heat riser tube) The 3697 WCFB has a nipple outlet at the top right rear to attach a vacuum hose. What is the purpose of this vacuum line?

Thanks Ray

[William C.]

Re: Vacuum Line

If it's the one I think you are referring, at the top of the air horn, it is to provide filtered air to the hot ait tube so that the air going thru the exhaust manifold to pick up heat and activate the choke opening is air that has passed thru the carb air filter element first.

[Mike McKown]

Re: Vacuum Line

Ray:

If I follow your post, it was to let filtered air go in the tube in the exhaust manifold to circulate back to the choke housing.

Mike

[Ray C.]

Re: Vacuum Line

Where would it connect at the manifold? The heat riser tube connects at the top. I can't find it in any of my books including a book on Carter carbs. Nolands 63-67 book shows the hose going past the exhaust manifold, but no connection point.

Thanks Ray

[Ray C.]

Re: Vacuum Line

Thanks!

I found a drawing in AIM 1965 and you are right on the money. Description: Pipe-Air Intake. The drawing only shows the pipe going under the exhaust manifold, attached by a clamp fastened by a spark plug shield bolt, not to a connection point. Where would the lower section connect?

Thanks for the help!
Ray

[Duke W.]

Re: Vacuum Line

The chole clean air hose from the side of the air horn connects to a u-shaped tube that disappears between the manifold and head and loops around underneth into the exhaust manifold. The exhaust manifold has a pressed in tube to seal the choke clean air system from exhaust gas while providing the requisite heating.

It is not uncommon after all these years for the internal tube to rust out. Also, since the u-shaped choke clean air inlet tube was just plain steel and was exposed to relatively high temperatures, they too have a tendency to rust and break off, which, perhaps, is why your engine does not seem to have this part.

Duke

[Brian Monticello]

Re: Vacuum Line

Maybe this will help you to visualize - I had the same question a few months back.

Keep in mind that the manner in which the clean air tube mounts is different depending on the year.


Brian

[Ray C.]

Re: Vacuum Line

Thanks!

Found it this evening. The location is right where your pictures showed. Now I need to find a source to secure the correct parts.

Thanks, Ray