I have a question about vacuum advances in a non-lean burn electronic ignition.

Perhaps I'm wrong, but I thought that at high vacuum, diaphragm movement pulls the distributor plate to advance the timing by the amount designed into the can, or on some, by adjusting the allen screw to match what you want. In this application, it should be 7-10 degrees.

The initial advance is 8 degrees with vacuum disconnected. At 2500 rpms, the mechanical advance is full and adds another 12 degrees. When I hook up the vacuum line, total advance jumps all the way to 60+ degrees at 2500 rpms.

If I have a non-adjustable vacuum control and the amount of vacuum advance is in excess of 30 degrees, does that more likely indicate a bad vacuum control or mechanical wear in the distributor?

Vacuum advance is double of what is marked on the arm....

If the arm says 6.5 you'll get 13 at the crank......

Adjustable cans adjust the vacuum needed to move the advance not the total advance (unless you crank it sooooo much that there's no possible way for there to be enough vacuum to open it up all the way)

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Ed
64 Valiant 225 / 904 / 42:1 manual steering / 9" drum brakes

30 does seem like too much for me.

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