It sounds like you have one with a vacuum brake. Must be a real early unit. some of them used a a vacuum brake that consisted of spring loaded piston that had a piece of cork one one side that rubbed against a round plate to pull timing out under certain conditions. When manifold vacuum was high it retracted the piston and allowed full advance. If the throttle was mashed at low speed the vacuum would drop and cause the piston to contact the plate which then retarded the timing. Virtually the same system as the early dual point distributors on the flathead Ford V8. Those were made by mallory for Ford. I would do away with it. Randy
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