THIS WILL WORK ON ALL XR50/70 CRF50/70 OR Z50R'S 1982 THROUGH 1999 IF YOUR USING A BIG DOME RACE HEAD OR A HEAD FROM AN OLDER HONDA 70, ONE WITH 22MM AND 25MM VALVES THE BIG DOME OLD TYPE HEADS WERE ON CT70 FROM 69 TO 81 AND ON ALL SL XL AND CL70'S OUR BARE HEAD HAS THE BIG DOME... S1196