A shim is better than messing with the screw for the simple reason that using the screw can damage the ALDA anaeroid or reduce the operating range. Actual bench adjustment is the shim, I think.

Peter

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1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!