BLOCK: 5 H.P. Briggs & Stratton Engine Only. Machining for clearance for rod, cam, and lifters are allowed. 2.630" maximum bore size. Welding to strengthen lifter bore and to repair broken rod damage areas only. No welding from cooling fins upwards.
BLOCK DECK SURFACE: Piston pop-ups is non-tech. Head gasket surface and top of block are non-tech items.
VALVES & SEATS: Steel valve seats only size and shape are non-tech. Aftermarket stainless or steel valves only, no titanium. Intake valve diameter 1.140" maximum. Exhaust valve diameter 1.005" maximum. Springs are non-tech item. No titanium retainers.
CAM: .400" maximum lift. Checked at the valve with springs attached as run.
PORTS: Porting is allowed. Port surfaces are non-tech. No addition of any materials to ports. No holes in ports. No machining of gasket mating surfaces on intake or exhaust.
CARBURETORS: Option #1; Briggs Raptor .715 bore with stock tank. No additional material may be added other than to block choke and vent holes.
Option #2; Animal Carb or Keihin carb (part #JH90) as cast from factory. Venturi maximum .792" vertical, .605" and .618" horizontal WKA animal no-go guages may enter but may not pass through bore. Items that can be removed through fuel bowl including nozzle are non-tech items.
INTAKE MANIFOLD: Used only with carb option #2. May not exceed 4" in total length. Fuel pump may pulse from intake or crankcase. Sealer with or without gasket is permitted.
CRANK: Stock 5HP Briggs & Stratton only. Stroke 2.437" plus or minus .010". Minor grinding for cam clearance is allowed.
ROD: Any aluminum is allowed.
PISTON: Any aluminum is allowed.
HEAD: Stock appearing. Any gasket sealer is allowed.
BREATHER: Any style but must vent into catch tank.
COIL: 5 HP Briggs & Stratton only. 2000 ohms min./5000 ohms max. No hot coils.
FLYWHEEL: NO CAST FLYWHEELS!!! 5 HP billet aluminum. ARC part #6620 or #6608 are allowed.
EXHAUST: With or without muffler. If no muffler is used header must have washer or flare added to end of pipe for safety. Pipe may not protrude into port. Header wrap is allowed.
FUEL: 100% methanol only. No additives. Will be compared to know legal fuel.