General Engine Rules

General Engine Rules: Applies To All Tractors In All Classes

  1. Only one engine per tractor
  2. Only 4 cycle, commercially produced air-cooled lawn mower/garden tractor engines
  3. One and two cylinder only
  4. Must use pump gas only from automotive gas station with no more than 91-93 octane. No octane boosters or other additives, alcohol, methanol, oxygenated, racing fuel of any kind, fuel from racetrack, airport or military base, (except modified class. see modified class specific rules for details)
  5. No fuel injection, turbos, superchargers, or pressurized fuel tanks
  6. Kohler accelerator pumps are permitted
  7. Carburetor must be stock OEM on engine used. Four carburetor modifications are permitted:
    1. Removal of choke plate and rod
    2. Throttle plate limiting stop can be ground to achieve full open throttle but must remain original size
    3. Fuel metering jets can be enlarged
    4. Intake side of carb may be mildly ported, bored and polished
  8. Engine may be bored to a maximum of .060 over stock (except stock class)
  9. No aftermarket internal engine components (Cams, pistons, valves, rods, crankshaft etc.) unless otherwise stated
  10. Custom or Copper Head Gaskets will be permitted
  11. Heads must remain stock. Shaving of heads is permitted (except stock class)
  12. After market valve springs will be permitted
  13. Ignition timing modifications will be permitted
  14. Crank Trigger ignition will be permitted (except stock class)
  15. Governors may be disconnected (except stock class)
  16. Aftermarket or custom air cleaners will be permitted (except stock class)
  17. Class RPM rules will be verified with SHS tach. A 200 RPM variance may be permitted due to specific conditions per Official’s discretion
  18. Headers and straight pipes will be permitted. Any non-stock pipes will be aimed up or out, not aimed at the ground causing a dust condition