How Determine Timed or Full Vacuum Advance?

[fine69]

How can I tell if my distributor has a timed vacuum advance or full vacuum advance?

The instructions that came with my Edelbrock AVS carburetor requires vacuum hose connections to different ports depending on the type of vacuum advance. My engine has not yet been installed.

Thanks.

 

[wishuwerehere82]

What distributor are you using?
A stock distributor would be full advance, using weights, springs and Vacuum.

 

[curtis]

Install a distributor that uses a vacuum advance and hook it to a manifold vacuum source. Select a vacuum can for the advance that matches up with your idle vacuum. The mechanical advance in the distributor should be capable of adding around 22 to 24 mechanical advance. The vacuum should add around 12 to 14. These are just baseline numbers that would fit almost any street engine, and should give you good power and cruise economy with initial advance of around 8 to 12 BTDC. The ported advance stuff was just a way for Gm to help attain better emissions.

 

[JohnZ]

How can I tell if my distributor has a timed vacuum advance or full vacuum advance?

The instructions that came with my Edelbrock AVS carburetor requires vacuum hose connections to different ports depending on the type of vacuum advance. My engine has not yet been installed.

Thanks.

Check the origin of the port connections on the carb baseplate; if they're BELOW the throttle butterflies at the idle position, that's full manifold vacuum. If they're ABOVE the throttle butterflies, that's "ported" (or "timed")vacuum (no vacuum at idle). You want full manifold vacuum at idle for the distributor vacuum advance can.

 

[fine69]

Check the origin of the port connections on the carb baseplate; if they're BELOW the throttle butterflies at the idle position, that's full manifold vacuum. If they're ABOVE the throttle butterflies, that's "ported" (or "timed")vacuum (no vacuum at idle). You want full manifold vacuum at idle for the distributor vacuum advance can.

Thanks to all for your replies.

John, the carburetor has the option of using either timed or full advance.. I just have to determine what I have. Is there a way to check by looking at the distributor?

Thanks again.

 

[JohnZ]

Thanks to all for your replies.

John, the carburetor has the option of using either timed or full advance.. I just have to determine what I have. Is there a way to check by looking at the distributor?

Thanks again.

The distributor has nothing to do with it, and doesn't know the difference. Just select the port on the baseplate whose orifice is below the closed throttle plate (blow smoke through them to find out where they originate).

 

[fine69]

The distributor has nothing to do with it, and doesn't know the difference. Just select the port on the baseplate whose orifice is below the closed throttle plate (blow smoke through them to find out where they originate).

Thank you, John. That makes sense. I'll select the option for full advance.