89'r
Yep that's what I see in the clymer, the '88 came with the 39 and the 89 with a 38mm. I know it seems backward, but heck anyone could've swapped out parts either way. I think I'm the fourth owner of my 2k 500 and your bikes have a few years on mine.
It shouldn't be a problem getting the carb tuned close, I should think.
CC3,
I know this sounds corny, but get a notebook and record your settings and jets, and keep it somewhere in the garage.
Before I did this I was constantly buying the wrong jets. Another thing is to see what the bike is doing as far as weather (time of year) and any other maintenance you've done. (guys looking to buy a bike like being able to see this also when it comes time to sell)
I'll look for a few links to help get you on the right track as far as what jets will get you where you want to be.
The Factory has to jet the bike on the fat side to be safe,(heck they end up all over the world) and it would appear your main is lean and the pilot is fat.
I would like to make one thing clear right from the git go.
There are a slew of variables that come into play.
Here are just a few, Weather, Altitude,condition of the engine, modifications,type of riding, how hard the rider is working the engine, pre-mix and ratio etc-etc.. so as much as I would like to be able to say
"Oh Yea, put in a 50 pilot above 70degrees and a 52 below and run a 168main above 70 deg and 170 below and you'll be Good to Go"
I really can't. If you are willing to do a bit of reading and hang with us a few posts I'm sure we can get you close,
and then you'll be surprised at how simple it will be to dial her in.
Here's a link to our Gallery where posted a bunch of stuff.
(You should be able to get the next two pages by clicking the arrow for next at top of the page.)
http://www.kxriders.com/coppermine/displayimage.php?album=267&pos=6 Tuck\o/
