94 to 97 wr's are based on the93/ 94 yz ,95yz's powervalve is trying to do more from the basic design and the 96 yz changed its frame and plastic. How it affected the bike or all of the details changing from these prevalent changes I am not sure. The only diferrence between the 94 wr and yz is wide ratio transmission, lighting coil, different tank and seat , an oring chain,rear wheel size,suspension settings, and probably a spark arrestor but not sure. As the yz's evolved the wr didnt except for maybe the Keihin carb and suspension settings. According to some people the 94-97 wr power would be a better motocrosser than a 96 yz and the 96 yz is an easier trail rider than the wr because of the way the yz cylinders and exhaust valves changed. You can easily bolt on the cylinder of any of these bikes as the engine cases and pistons are the same. But would be very expensive to match all parts , reed valve, head,exhaust valves,pipe and possibly ignition timing<cdi>to have parts that are designed to work with each other properly for decent power. Yet it is relatively cheap to modify<port ,head and powervalve mods> to have them feel all the same.
interesting note is that the wr stator with a lighting coil is actually cheaper than a yz stator with no lighting coil. As with some of the different parts that are actually interchangeable with no performance loss or modification.<my parts guy loved me with all these questions when i was bugging him :eek: >
I am in no way an expert but I have done a little bit of research by my reading of Eric Gorr's performance handbook,studying parts microfiches, bugging my yamaha dealer, and the rare occurance of me actually buying a part that is not an actual 94 yz part becasue one of the other years/ models was cheaper