The Stovebolt Site Forums The Shop Area Engine Shop 1960 rochester 2G distributor vacuum question

I am trying to figure out where my distributor vacuum line goes. I have a 1960 283 with a Rochester 2G carb. The vacuum line was hooked up to manifold vacuum when I got the engine. The only vacuum port I find on the carb is a large one in the throttle plate thet appears to be for power brakes. I did find another brass screw in plug just below where the fuel line goes in. it appears to be a place to get ported vacuum but I am not 100% certain it is a vacuum port. Anybody know? I can not fire the engine up to test it.

Some of the 283's and 327's used full manifold vacuum to the distributor, occasionally supplied through a hollow mounting stud for the carburetor base. Normally, a ported vacuum source would be in the throttle plate housing just above the idle mixture screws. I doubt that something near the top of the float chamber would be a vacuum port, but it's a possibility.
Jerry

Thanks for the info Jerry, I do have the hollow stud and that is where the vacuum was routed to. I will just leave it there. The port near the float bowl is just above the throttle plated and I found a couple of pictures where it appeared the distributor vacuum line was plugeed into.
Shane

OK, it looks like your carb could be set up either way, if there's a port about venturi level or slightly below it. If you pull that plug and probe the passageway with a piece of thin wire, you'll probably find that it connects to the bore just above the throttle plates. That keeps vacuum off the port during idle, and gradually applies vacuum to it during part-throttle operation. I looked up the distributor specifications for a 1960 283, and the vacuum advance should start moving with about 4-6 inches of vacuum applied to it. 14-18 inches will give it full movement, so full vacuum at idle will result in about 15 degrees of advance at the crankshaft immediately after the engine starts, even at idle. The ported vacuum won't begin advancing until you tip the throttle in, and by midrange RPM at light throttle, you should have full movement on the advance. Stepping on the gas enough to lower the vacuum below the venturi allows the spark to retard during acceleration to prevent detonation. To get an accurate initial timing setting, disconnect and plug the vacuum line at the distributor while checking the timing.
Jerry

Jerry,
After reading your latest post, Should I go ahead and put it to the ported vacuum or leave it on the manifold. I have alway had the advance on ported vacuum on every othe engine I have had.
Shane

If you can find an original vacuum diagram, it would probably be wise to start with what the factory engineers chose. Of course, in 1960 we still had leaded gas with much higher octane ratings, even regular was blended for compression ratios above 9:1. I'd try both ways, ansd see which one gives the best power and/or gas mileage. Back when I could still hear it, I would listen for detonation and tinker with the timing until I could pull a long, steady hill at meduim throttle without getting any spark knock. Now I have to take my grandson along to be my listener!
Jerry

I was leaning towards the ported myself base on the crappy gas that we have now. I will try it both ways and see what works best. Thanks for all your help.
Shane

I find with an auto matic trans. it works better on ported vacuum. Manual trans works good with full manifold vacuum.