You can't adjust the timing on a 420. The distributor has adjustment ONLY to set up where the rotor points to the electrodes. The ignition is fired by a crankshaft sensor in the rear of the engine.

The vacuum may be missing going to the EZL...Check that first.

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Benzmac:
Donnie Drummonds
ASE CERTIFIED MASTER AUTO TECHNICIAN
MERCEDES SPECIALIST 11 YRS