MP DISTRIBUTOR TIMING CURVE 340

Bewy said

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.

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I agree with this approach. Another helpful technique is to use a mity-vac (hand vacuum pump) when adjusting the VA can as it will show what inHg corresponds to the amount of advance added. Use a vacuum gauge on the engine while driving to find what the manifold vacuum is at idle and cruising speeds and tune the VA accordingly. All done with the engine in the car of course, it's pointless to try to tune vacuum advance on an engine stand with no load. In my experience it's an iterative process (trial and error) to find what your engine likes best but can really make a difference in throttle response, driveability and fuel economy.