Posted by Fargen Bastage on October 23, 2007, 9:11 pm
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.
Posted by Albrecht via MotorcycleKB.com on October 23, 2007, 9:29 pm
Fargen Bastage wrote:
>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.
The theory was that if the center plug got bridged with a bit of grit and
stopped firing, you could get back into the race by whipping the plug lead
off and sticking it on the other cylinder.
Another thing you could do was install a cable-operated compression release
in the second spark plug hole and that was very helpful when descending steep
hills.
Using two different heat range spark plugs wasn't necessarily a good idea,
because the cold plug might foul while the hot plug was causing preignition.
You couldn't win that game.
--
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>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.