After a couple of hours of reading I still have a question. I have a stock 390 2V with an Edlebrock performer 4V intake and carb and Mallory dist. It runs ok but not great thats one reason Im headed down this path. I know other things may come into play but I want to concentrate on timing first. Let me make sure Im on the right track first.


Make sure my timing ring hasnt sliped by veryifing actual TDC of piston with TDC of timing ring.

The specs on my Mallory say 24 degrees between 3000-3200 rpm. So, I rev to 3000-3200 rpm, or until it no longer advances, and set the timing to between 36 and 38 degrees (vacuum disconnected and capped). If my idle is set correctly to 650 rpm, the timing should read between 12 and 14 (36-38 minus the 24 Mallory says it will advance). Regardless of what it actually says, that number will be my initial timing and I should mark it or remember it for future timing adjustments.

Now for the part Im not clear on. Vacuum advance. Most of the reading I did was on the argument between manifold and ported. That argurment doesnt interest me at this point. My question is, whats the procedure for checking and adjusting (if possible) vacuum advance?

 

To check your vacuum advance you can have the engine running and have the vacuum hose from the distributor in your mouth and suck on it to see if the mechanism is working. Hook up the vacuum to either the ported or manifold vacuum port as designated by Mallory.

 

I know its working, I want to know if its working correctly. I want to know if its providing the proper amount of advance.

 

The proper amount of advance depends on your engine and what it likes best. In order to make the engine run best you need to know what Mallory wants you to hook the advance to. The stock system usually uses ported vacuum from the carburetor which limits the amount of vacuum to the distributor. Mallory may want manifold vacuum which will give maximum advance at an idle and at cruising speeds.
I suggest that you set the timing at 38* at 3.000 rpm and see how it runs. You can disconnect the vacuum at idle and see what your initial timing is at then. You can the adjust up or down to a max of about 42* and always at 3,000 rpm as nearly all systems are all in before 3,000 rpm. If the timing is still advancing at 3,000 rpm you will need to find the point where it no longer advances and use that as the place to set your maximum timing.
You are always safe setting to your maximum timing as there will never be more unless you change it.