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Apr 26th, 2026 | | AD Chevy Trucks  Over 6,000 pictures Brad Allen has an awesome collection of Chevrolet factory pictures that he has set up from film strips. Check them out!
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#30481 05/14/2004 2:25 AM | Joined: Mar 2004 Posts: 734 Shop Shark | | Shop Shark Joined: Mar 2004 Posts: 734 | I've got the vacuum advance hose connected to the right port on my Rochester 2G (replaced the 1 bbl on my 292 and also added headers and Offy intake) however, it seems to have as much vacuum as the manifold. Not sure what's going on there. So, when I take the hose off, plug it and set timing around 6 degrees, it's back up in probably the mid - high 20's after reconnecting hose. This can't be normal. It's getting too much initial advance 'cause of vacuum right? Aside from trying another carburetor in which the ported vacuum actually works, is an adjustable vacuum advance the answer? If so, is there one available for the inline points distributor? | | |
#30482 05/14/2004 3:50 AM | Joined: Sep 2001 Posts: 85 Wrench Fetcher | | Wrench Fetcher Joined: Sep 2001 Posts: 85 | Some engines use ported vacuum and some use manifold vacuum. I am running a 78 305 in my truck, with 2 GC carb also. My engine uses manifold vacuum as per the factory set up. However, the orignal car had a vacuum switch that limited vacuum until high gear. A pollution lowering device. My carb also has a smaller ported vacuum below the manifold port.
I have a 79 Chevy Caprice at school with the same engine and set up.
I am running my truck at 8 degrees BTDC and using the manifold vacuum port. I get a slight ping on Heavy accel, but that is all. | | |
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