I'd just like to add a note to the responses that have already been made. There is a question regarding resistor or non-resister type plugs. Remember, when these motors were new they came with copper core ignition wires and a screw on resistor (brown bakelite housing--or the later type with a metal shield as on early B21/23 motors). If you have resistor wires or plugs you don't need the screw-on type as well-- or -- conversely -- if you have non-resistor plugs--you'll need a screw-on resistors or resistor type wires. Personally I prefer NGK plugs after working at Honda where the method to set carb float height is to use the external adjustment to flood the engine then back off a set amount. Even after flooding, the motors restarted without problems. -- Dave