ignition advance, not model A

I wonder where a person could find the specs for that distributor? Often times there will be 2 different springs, the weaker one to allow some advance as soon as the engine starts, then the stronger one to allow more advance with more RPM.

One also needs to know the function of the vacuum pot. Some are designed to give advance, and some are designed to give retard, depending on if the vacuum is manifold vacuum, or venturi vacuum.
 
Some are Venturi vacuum just for the fact that it's not supposed to have any vacuum at idle. (No advance).
The diaphragms I have seen that retard also have 2 vacuum hoses to them.
They can be tested with a vacuum pump
 
The vacuum on this Plymouth is ported below the throttle plate on the carb (updraft)
So it has no vacuum at an idle, as soon as the engine speeds up from an idle, the vacuum advances the distributor. Plymouth description was this feature was to ensure the engine is in full retard in the event you had to hand crank. The vacuum advance is working, when you open the throttle the whole distributor moves.
I suppose I should reasurch as see if someone knows what the total advance was supposed to be. Information on these old Plymouths is not as readily available as the Ford products.

Dave
 
The oldest book I have goes back to 1935. It said the timing mark is on the vibration damper. Here is what it has to say. 4th line ATDC. But I know yours is older so might be different.
 
From the Standard Manual pdf.

http://restorecarsclassifieds.com/w...1931+plymouth+ignition+timing&search_kind=and

IGNITION
Rotation, R. H., Top View
Delco-Remy, 629-A
Breaker—Contact separation .020 inch.
Contact Spring Tension—18 to 20 oz.
Timing with MOTOR GAUGE—IMPORTANT! Time ignition in
full advance position. Remove No. 1 spark plug, and attach
MOTOR GAUGE, using adapter No. 104 and rod No. 2. Slowly
hand crank engine until No. 1 piston is coming up on compression
stroke. Stop when .050 inch before T.D.C, as indicated on Gauge.
With rotor opposite No. 1 Dist. Cap Terminal, breaker points
should just open.
Spark Plugs—Metric (AC type G-12); Gap .022 inch.
Firing Order—1-3-4-2.
Manual Advance—22 degrees (on Flywheel).
Automatic Advance—20 degrees (on Flywheel).

Also, some ideas:
http://www.1948plymouth.info/28Q29U/index.php?topic=870.0

Interesting case this ...
 
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