A vacuum gauge is plugged into any clean (unrestricted) source of intake manifold vacuum. Do not use any carburetor fitting, rather, use the intake port for, say, the PVC or brake booster. Then, with the engine warmed to operating temperature,disconnect the distributor's vacuum advance hose and plug it, and at correct engine idle speed slowly rotate the distributor (CCW retard; CW advance) until the vacuum gauge needle reaches highest point. Then drop back one point; tighten distributor. That will give optimum timing at idle speed. Re-connect the distributor vacuum before road testing. This method pre-supposes the carb mixture has been attended along with the customary tune-up observances. The vacuum gauge, and the compression gauge, are invaluable when trouble-shooting engine performance problems. A vacuum gauge mounted in the cab aids in extracting the last ounce of gas mileage driving performance as well. As for that old fuel pump, well, if attached to a siphon hose it beats the heck out of an unwanted drink.
