Two spark plugs - One cylinder

 Two spark plugs - One cylinder

I have a circa 1970 Yamaha 175 enduro motorcycle that has one
cylinder, but two spark plugs.  I've never had a spark plug wire on
the 'other' plug and it's run just fine.  Now, many many years later,
I'm trying to fix this bike up for my son and I'm wondering, "What the
heck is this other plug for???" I don't even think there is another
wire.
Thanks much for any help you can provide.

 Hi
  IMHO,one will be for gentle off road use,the  other for fast road
use..simply swap the plug lead to the one that suits what it's being used
for.
  The other idea may be to run  two identical  plugs on a coil with 2
outputs...twin plugging the head helps with combustion etc

 the idea was years ago that if one plug fouled out you could just put
the plug wire on the other plug and life would be good again,,,,it
really didnt work that good though because the plug that wasnt fireing
would usualy be fouled also,,,,,,,,,,,,,,tom

 the idea was years ago that if one plug fouled out you could just put
the plug wire on the other plug and life would be good again,,,,it
really didnt work that good though because the plug that wasnt fireing
would usualy be fouled also,,,,,,,,,,,,,,tom

 yes indeed, I remember once needing to use the other plug and it was fouled
although in those days plugs just "gave up" through use and at least the
other worked, if messy. By that takes me back.

Shawn (all the more reason to love 4-strokes) XT 500