I seem to recall reading about my T250II that if the charging system and battery weren't REAL good, you'd get enough voltage drop for the left side points that it just had a weak to no spark. Something about the way things are wired up stock or whatever. I had the same problem on the left side and cleaned all contacts and new battery and all I know is that problem went away. I think they are magneto's to boot so not sure why the battery would make a difference, but did what I had read and it worked. The key thing that I read was the left side suffered first, odd.
2006 HD 1200C, 2006 Tri Scrambler, 2001 Duc M900, 2001 Hon XR650L, 1994 HD Heritage, 1989 Hon Hawk GT, 1978 Hon CB750K / sidecar, 1977 Guzzi 850 LeMans, 1976 Hon CB750K, 1965 Hon 305 Dream, 1973 Nort 850 Commando, 1971 Tri Trophy 650, 1970 Hon Trail 90, 1970 Tri Tiger 650, 1973 Hon Z50, 1984 Yam Virago 1000, 1981 Hon Passport 70, 1970 Suz T250, 1971 Yam RT1 360, 1965 Hon CT200