Engine 600cc 4 cylinder 4 stroke as comes on a stock production bike for public sale in the
U.S.A. No current year production engines. Except as noted, all internal and external engine parts must remain stock with no modifications, metal removal, blueprinting.
Valve seat inserts may be reworked. Valves must remain as produced with no modifications.
Valve springs may be shimmed with standard or aftermarket shims.
Cylinder head combustion chambers may be cleaned by bead blasting with valves seated in
place. Intake and exhaust ports may not be bead blasted.
Cylinder head gaskets may be replaced only with original equipment manufacturer’s stock
parts (All 3 layers of the head gasket must be used). All other gaskets may be replaced with
duplicate aftermarket parts.
Light cleaning of gasket surfaces with steel wool, Scotch-Brite, etc. is allowed.
Transmission gears may be shimmed only for the purpose of proper engagement. Standard or
aftermarket shims may be utilized. Aftermarket cam chain tensioner allowed for safety of
Fuel injection engines must run carburetors. Fuel injection engines running carburetors may
change all fuel metering devices to tune fuel curve, Billet intake boots allowed.
Modification of oil pan & pick up allowed or aftermarket ok.Modification to thermostat cover allowed or aftermarket ok.
Modification to water pump Cover allowed or aftermarket ok.
Any air box, stock appearing CDI, aftermarket washable replacement air filter.
Any 600cc OEM CV carburetors (no flat slides allowed).
Restrictor plate must have hole diameter .750 inside, outside must be tight against inside of
boot, absolutely no allowance, plate must be against carburetors. Restrictors must be flat, no