My 86' 250 was doing exactly what yours was doing. I always wondered what could be wrong with it. This is good stuff.

I thought this might be useful to somebody.

http://vintagesleds.com/library/manuals/misc/vmmanual.pdf

Actually read it, just don't dismiss it cause it's not the exact model pictured. It explains how the different types of carbeurators function, dimensions for identifying different models, how to jet, and it breaks things down in a way that's understandable about everything.  It's good stuff.

How about this?

http://www.keihincarbs.com/carbs/pwk/gate.html

Looks like I got some more reading to do!

Quick update, I stuck a #38, still rich. Raised the clip from middle to 2nd position and sounds better, but still rich. I will pick up a #35 pilot (the smallest one they make for pwks) and a slightly thicker needle, if I find one, and see how that combo works...

The needle has alot to do with pilot you run.  I ran a dgl needle I would have to run a pilot in the 60 to 63. Then when I had egg in it wanted 42 to 45..   That is the big thing finding the right needle to run on the pwk.

I'd give duncan racing a call. They have all the keihin needles jets and they can recommend starting jetting specs since they sell the 39 pwk.

As said earlier the needle makes a big difference. On my 250 the dgh needle was to lean in the low to mid and it would ping, dgg richened it up.

I ended up buying three off of amazon for around $22 w/ shipping included. They are genuine keihin, not oem needles. We'll see what works best when I get them and test them, and i'll just sell the ones I don't need.