Prior to 1990, most vehicles were equipped with carburetors which mixed the gasoline with air before the fuel entered the engine. A common problem with carburetors is the frequent adjustment of the fuel and air mixture required to keep the engine running smoothly. Changes in gasoline or altitude, or just vibrations from the running engine can require an adjustment of the carburetor. As with most stock systems manufactured during the 1960's, the idle air-fuel mixture and idle speed are the only two basic adjustments for the carburetor on a 1967 Ford F-100 pickup truck.
Start the engine and allow it to run until the it reaches its normal operating temperature, as indicated by the temperature gauge in the dashboard.
Pull the rubber vacuum hose from the side of the carburetor body and attach the hose from the vacuum gauge in its place. Adjust the idle mixture screw on the body of the carburetor with a screwdriver until the reading on the vacuum gauge matches the setting specified in a service manual for your carburetor and engine combination. Back out the screw to increase engine speed and vacuum reading, and tighten it to decrease both. Remove the vacuum gauge and reattach the vacuum hose.
Adjust the idle speed of the engine by turning the idle speed screw, which is set into a plate as the base of the throttle linkage. Use a screwdriver to tighten the screw to increase idle speed, and back it out to decrease idle speed. Listen to the sound of the engine as you turn the idle speed screw, no more than a 1/4-turn at a time, in each direction. Adjust the screw until the engine is running the smoothest. If the adjustments don't help, the carburetor needs to be rebuilt.
