Power Valve Control Solenoid Valve

Disconnect vacuum hose from power valve and connect vacuum pump. With ignition on, apply vacuum and listen for clicking sound from power valve. If no clicking sound is heard, replace carburetor. If clicking sound is heard, start engine.
Warm-up engine to normal operating temperature. Disconnect hose from power valve and connect vacuum gauge to hose. There should be no vacuum. If no vacuum, proceed to step 4).
If there is vacuum, check for voltage at Yellow/Black wire of No. 2 control box connector. If there is voltage, replace power valve control solenoid valve and retest. If there is no voltage, check fuse, wiring, and speed sensor, and retest.
Raise and support front of vehicle. Set parking brake and block rear wheels. Place vehicle in 2nd gear and check for vacuum at power valve hose No. 14 above 10 MPH. There should be vacuum. If there is vacuum, proceed to step 6).
If no vacuum, remove control box cover and check for voltage at power valve control solenoid valve. If there is voltage, replace vacuum switch B and retest. If there is no voltage, replace power valve control solenoid valve and retest.
With vehicle still in gear, and speed above 10 MPH, disconnect vacuum hose No. 1 from control box No. 2 at vacuum hose manifold. There should be no vacuum to power valve (hose No. 14). If there is no vacuum, system is okay. Reconnect vacuum hoses.
If there is vacuum, check for voltage at vacuum switch B with vehicle speed above 10 MPH. If there is no voltage, check fuse, wiring and speed sensor and retest. If there is voltage, remove control box cover. Check for continuity between terminals of vacuum switch B with vacuum hose No. 1 disconnected.
If there is continuity, replace power valve control solenoid valve and retest. If no continuity, replace vacuum switch B and retest.