Large RPM and Vacuum drop when shifting from park to gear

Mattax said

The timing is moving because the distributor's mechanical advance begins somwhere above normal idle speed.

Click to expand...

Here's an example of the timing changes with rpm due to the mechanical advance.
Initial timing for for this engine/distributor combo was 0*, plus or minus 2.5*


You've measured around 15* at 900 and 20* at 1100 rpm.
Lets put that on the same graph paper so you can see why that would be normal advance for many distributors.


An original Chrysler distributor will have a metal tag on the side.