MP DISTRIBUTOR TIMING CURVE 340
The VA spring [ rate ] adjustment using the Allen Key [ AK ] .
One of the biggest reasons MVA gets a bad rap such as, 'It didn't work for me' is because it was used with a low vacuum cam & the AK was not adjusted. More a problem with auto trans.
Turn the AK fully CW [ softest setting ].
Engine idling, in gear if auto, make sure the timing is steady. Job done.
If you get light throttle ping, turn the AK 2 turns CCW. Recheck timing. Keep going 2 turns CCW & rechecking timing. When timing becomes unsteady, go 3 turns CW.
With cams that have really low idle vac, it is better to use more initial & less MVA to get the desired idle timing.