Simplicity RTH Series Operator's Manual page 33

Troubleshooting
4. Engine stalls easily with mower engaged.
A. Tractor ground speed too fast. Use lower gear.
B. Engine speed too slow. Set for three-fourths to full speed.
C. Cutting height set too low when mowing tall grass. Cut tall grass at maximum cutting height during first pass.
D. Discharge chute jamming with cut grass. Cut grass with discharge pointing toward previously cut area
5. Excessive mower vibration.
A. Blade mounting screws are loose. Torque to 50-70 ft. lbs. (68-76 N.m). See Normal Care section.
B. Mower blades, arbors, or pulleys are bent. Check and replace as necessary.
C. Mower blades are out of balance. Remove, sharpen, and balance blades (see Normal Care section)
6.
Excessive belt breakage.
A. Belt tension too tight. Readjust belt tension.
B. Bent or rough pulleys. Repair or replace.
C. Using incorrect belt. See your dealer.
7.
Mower drive belt slips or fails to drive.
A. Mower drive belt out of adjustment. See Adjustment section.
B. Mower drive beit broken. Replace belt.