z Unsatisfactory performance If the governing system functions poorly, perform the following tests. z Insufficient magnetic speed sensor signal A strong magnetic speed sensor signal will eliminate the possibility of missed or extra pulses. The speed control unit will govern well with 0.5 volts RMS speed sensor signal. A speed sensor signal of 3 volts RMS or greater at governed speed is recommended. Measurement of the signal is made at Terminals C and D. The amplitude of the speed sensor signal can be raised by reducing the gap between the speed sensor tip and the engine rind gear. The gap should not be any smaller than 0.020 in (0.45 mm).
When the engine is stopped, back the speed sensor out by 3/4 turn after touching the ring gear tooth to achieve a satisfactory air gap. Maintenance of Major Components - 115 - Symptom Test Probable fault Engine overspeeds. Do not crank. Apply DC power to the governor system. Actuator goes to full fuel. then, disconnect speed sensor at terminals C & D. – If actuator still at full fuel → speed control unit defective. – If actuator at minimum fuel position → errorneous speed signal. Check speed sensor data. Manually hold the engine at the desired running speed. Measure the DC voltage between terminals A(-) & F(+) on the speed control unit. 1. If the voltage reading is 4.0 to 6.0 VDC.
a) SPEED adjustment set above desired speed. b) Defective speed control unit. 2. If the voltage reading is above 6.0 VDC. a) Actuator or linkage binding. 3. If the voltage reading is below 4.0 VDC. 4. Gain set too low. Actuator does not energize fully. Measure the voltage at the battery while cranking. If the voltage is less than 15 V for a 24 V system, replace the battery if it is weak or undersized. Momentarily connect terminals A and F. The actuator should move to the full fuel position. 1. Actuator or battery wiring in error. 2. Actuator or linkage binding. 3. Defective actuator. See actuator troubleshooting. 4. Fuse opens. Check for short in actuator or actuator wiring harness.
Engine remains below desired governed speed. Measure the actuator output. Terminals A & B, while running under governor control. 1. If voltage measurement is within approximately 3 volts of the battery supply voltage, then fuel control restricted from reaching full fuel position. Possibly due to interference from the mechanical governor, carburetor spring or linkage alignment. 2. Speed setting too low.