Having fun with timing
. The MP electronic distributor only had one spring installed and from what I can tell from the spacing on the weight limiter slot it may only advance about 20 degrees mechanically possibly a bit more. The slot is not much larger than the 18 degree slot on the FBO disk.
Too bad someone messed with it.
The older Chrysler built DC and MP distributors came with very good curves in them for their specific purposes.
Both could be tweaked by adjusted the spring perches but all this seems to have been a secret (or been forgotten)
There should be a primary spring and a secondary spring. The primary spring has tension on it even when the distributor isn't spinning. The tension force determines the rpm when the advance weights will begin to move out.
The secondary spring engages when after the weights have moved the advance governer (slotted plate) X number of degrees.
The 'tach drive' units were set up for easy starting and winning drag races, stock eliminator type racing. A bit more initial tension will make a more consistant idle.
Tach drive Race Distributor
The street/strip units (with vac advance) seem to get best idle with a close to factory high performance cam. Over 220 @ 50 duration the curve should be shifted a little so a higher initial is obtained for stability at idle.
Here's some examples of guys adjusting the curve on Chrysler built distributors.
Here as Rick as he works through and posts the effects of his changes
And
an example of how that changes a bit with different combustion characteristics for later engine
I spill the beans on shaping the curve
here
Earlier in that same thread are
links to videos illustrating why the heavy secondary spring is important with electronic ignition.