Jimmie,
Just for clarification, when you step on the gas/open throttle plates the engine looses vacuum and retards the timing, timing does not advance until the engine speed increases and builds vacuum. At idle a stock engine should produce around 16-18" of vacuum and be steady, this increases/advances the timing, when you open the throttle plates the engine looses vacuum/retards timing to allow the engine to respond/accelerate with the drop in cylinder pressure. As the engine responds/accelerate vacuum will increase/advancing timing.
If the timing does not retard when the throttle plates are opened the engine rpm will drop or cause a flat spot before the engine speed will increase.

Mark D.

1968 W200 Sweptline
1969 D100 Utiline
1971 D100 SE Sweptline
1993 D250 Club Cab Sweptline
1986 W250 Cab & Chassis
1978 D300 Sweptline

E. Brookfield, Massachusetts