Re: '..eighteen years of technology..'
You mean eighteen years of pretty much the same thing year after year?
Out of the box, the KDX is a barbie doll play bike. I don't know if that was the case in '87.
Seeing as my '00 KDX 200 can chew on a brandy new CRF250X's rear..and pass it on occasion, I think the KDX can be made to run pretty well.
Maybe your '87 is unique and something to be simply cherished. Machines do that sometimes..they just work better than they have any right to.
Oh...the Boyesen RadValve is a complete goober, waste of time, sand down the proverbial rat hole, $$ flushed down the terlit, AND an absolute POS.
This is a one year old RadValve reed:
If it worked well
before it came to this, that would be one thing. But, it didn't.
I've seen other's RadValve reeds that looked worse than mine!
Cheers!