Motorcycle Repair: Spark plugs, sport bikes, bill silver

Question
Hi Mr. Silver
I have a 1964 CB72 250cc Hawk and it was set up for racing in the 1960's. The bike has numerous cyb parts and a cyl. head that takes some real small spark plugs (NGK C-9h)the plug has the Hm logo on it and I can not find them anywhere. Please email me if you know where I can find these spark plugs. Or if you know of a replacement plug that will work.
Thank you very much. Sincerly Gary Higby

Answer
Gary, sounds like you got some really cool stuff there! The C9H plugs were only used on the 1961 250-305s. I went to  www.ngksparkplugs.com and found:
P/N R0161-10  Stock # 4778 gap at 0.028"

A lot of late model sport bikes have 10mm plugs like that, but they are all resistor types.

FYI we have developed electronic ignition kits for CB/CL72-77s. They are a must for accurate ignition timing.

Bill Silver www.vintagehonda.com