Steve, good to have you on board, when you add weight to the fly wheel it slows how fast the rpm's spin up. Your bike will still go the same top speed. The weight takes the on/off power hit the K5 has and makes it more manageable. Most people ad the weight for tight trails or wooded riding areas where you have allot of turns and or stop and go riding. I have one on my K5. It also makes the bike easier to start. Here's a pic of my weight. http://www.kxriders.com/coppermine/displayimage.php?album=89&pos=0
When looking for wheels the 1997 and up have 3 bearings. 2 on the drive/sprocket side. You need to make sure it will fit your bike before buying.
Here's a good place to look up parts,
http://www.kawasakipartshouse.com/?gclid=CILPs7nG5I4CFSCTWAod9A30RgLook up the part on the 86' motor then look up the same part on the 87' if the numbers are different most likely they won't interchange. Some times the numbers change but the part doesn't. But that's rare.
Now for the part where I ask you, a new member a favor. This site has been up since sometime in 02' or 03' and it's free for the world to join, look at, trade info, meet new KX riders and have a good time.
All I ask of you, is to use the search function so we don't repost the same questions over and over. The flywheel weight is one of those questions. Sometimes the search just does not give the answer you need. I did a search on flywheel weight and even this post showed up. As far as finding wheels, post that in the Wanted section, you'll get more response.
With your help we'll keep this site running smooth.
Thanks,
Danger4u2