Vacuum retarded dist?

[LRMAN]

I was working on the timing of my engine today and found the vacuum from the carb is actually retarding the timing while the mechanical is advancing it. Is that correct?

I disconnected the vacuum from both the dist. and the carb and blocked them both. Then I set the timing to 6° BTDC. When I revved the engine I saw the timing advance(pulley mark moved counter clockwise). When I reconnected the vacuum hose the timing retarded below TDC(pulley mark moved clockwise). And moved further clockwise when revved.

[kevkon]

The vacuum advance works on manifold pressure. Vacuum ( negative pressure) is highest under partial throttle low loads and lowest at open throttle. The reason you set the timing with the vacuum blocked is that the timing would be advanced from the vacuum pot under closed/partial throttle position. What you saw was the vacuum advance coming off as you opened the throttle.