fouls one plug on cold start

[1957steve]

xs1 , Many years ago ,when i used to start this bike,it would allways foul one of the plugs.on a cold start.Id clean it ,then it would be fine.It would do the same thing next time after resting.

 

[gggGary]

Typical weak 12 volts gassy carb points ignition thing. add a valve seal letting a bit by while setting and and.... Yamaha changed the plug specs later try an NGK bp7es

this thread might shed some light. http://www.xs650.com/forum/showthread.php?t=43259