Mark -I think you should test for (total) vacuum advance by setting your inital at idle with no vacuum. Then observe the change when you put full manifold vacuum on the distributor port. I don't think reving it up will do any more for you than a good idle tune. 

The available vacuum to run the test ought to be at maximum when you have the idle mixture set "just so" and the valve lash in good order. You might get a bit more by jacking up the initial advance a bit. 

Charlie's suggestion is a good one too - but I've never had access to a vacuum pump. 

 
 Steve Metzger       Tucson, Arizona

Another method is to get a hand vacuum pump, and manually increase the vacuum to the diaphragm and check the advance.


Lawrenceville, GA

Hello Steve,

The light I have is the basic one.If I can get some accurate as possible marking on the damper how would I figure out how much the vacuum advance is giving?Hook up the vacuum line and run motor to 3000RPM and see what the total advance is.Disconnect the vacuum line and run again and see what centrifugal advance only is.Deduct centrifugal from total advance would tell me how much the vacuum advance is giving me.Correct?Thanks

  

Mark - There are a couple of methods available - measuring and marking the damper is one - sometimes hard to get in there after everything is together. But sometimes its the only way.

Second is to use a "dial back to zero" style of timing light. Mine is an old Sears unit and seems to work well, many do - but I have heard compaints about the accuracy of others. Its a pretty useful instrument if you are going to set-up a distributor right there in your driveway. Better to read the directions for the unit you get than listen to me! But it will let you set the initial timing, measure the centrifugal advance and the total timing. At idle, you can see your initial - then plug in the vacuum can and measure the increase directly.

 
 Steve Metzger       Tucson, Arizona

I installed the later distributor on mine last year and now I pretty well have the carb dialled in as far as jet size.I only have a basic timing light without the dial thing on it.How can I figure out how much vacuum advance I have and how much centrifugal advance I have?What are the suggested settings?What can I do to change the centrifugal settings?This distributor does not have the nut on the end of diaphragm so I am guessing the  vacuum limit can be adjusted with an Allen key.I wish I had put a degree tape on the damper when I had it off last year.Hard to get accurate marks after 10 degrees where the factory marks end.Any input appreciated.Thanks