Spark plugs are getting killed pretty fast

Hello all. I have recently purchased a 1980 Yamaha 650 Heritage Special
from a friend for a whopping $100.00. After doing so, I had to do some work
on it to get it up to speed. New handlebars, new cables(clutch, front
brake, ect.), new output shaft seal, a whole lot of cleaning up, and an
entire upper block rebuild (Head gasket was blown, so I figured I might as
well change all the gaskets). After doing all this, my spark plugs wore out
in a couple of weeks. I took it to a cycle shop in my area, and found that
after cleaning out my carbs, their sync was way off. So they hooked the
bike to their machine, and set the carbs to sync at 14cm, just like they're
supposed to. I bought more spark plugs, and it ran like a dream come true.
Then, about two weeks later, the spark plugs did the same thing. I'm
running out of ideas as to why this is happening. Any insite would be
greatly apprecieated.

Johnny wrote:

 > <snip> After doing all this, my spark plugs wore out
 > in a couple of weeks.

Define "wore out". Covered with oil, rich mixture, burned, melted,
broken, what?

I've a feeling that if you find the meaning of "wore out", you'll also
find the cause of the problem.

LittleJohn
Madison, AL