I bought a used 1996 XR400 CDI, (actually two) and a 96 XR400 flywheel, since the 96/97s seem harder to come by and are more expensive. These were very reasonably priced so I bought the trio. As has been discussed around hear before and what I have found elsewhere to substantiate the info between the 96/97 & 98-2004 year models, the 96/97 North American CDI version is supposed to have further advanced timing over the 98 & newer versions. This makes the 96/97 version, the one to have. The euro/Aussie bikes kept with these 96/97 versions. The flywheels are different as well between 96/97 & 1998-2004 models. As for the XR400 flywheel, I got it mainly to look at the size difference and position of the pickup tab compared to the 650R. I also wanted to see how similar it is in general to the XR650Rs flywheel. I would be curious to compare notes with a 98-2004 year model XR400 as well, if someone wants to pull one & compare notes just the same. I do have my flywheel lightened and I figure the 96 400 CDI is going to be a good synergistic addition to this mod.. I fitted the 400 CDI on the bike last night and ran it in the garage. I did not ride it out on the street. Even with it installed on the bike and just letting it run at idle and revving it up, you can tell the difference in how it runs. The first thing that I noticed and what surprised me, was that the bike actually runs a little higher in the RPMs at idle between the two CDIs. To be sure of this, I switched them back and forth about 3 or 4 times. I think what I am seeing is the slight advancement at idle is what makes this difference. Not only does it idle higher, it actually seems to run more evenly or rather smoothly or cleanly. I have to check it out further to see if when I lower the idle speed down to where it is with the stock unit whether it still seems to hold a steadier and/or crisper idle. Now, as far as free revving when whacking the throttle open, it surely jumps up further into the upper revs. It does sound different up there. It has a sort of raspier crackling sound when it hits the upper revs and starts to come back down. By going back and forth with the CDIs, and going back to the stock unit, it sounds muffled and held back for sure in comparison to the "96 400" when it hits the upper revs. That's a given of course because of the rev limit being higher. Now, the higher rev limit alone is not the real or priority benefactor for this mod.. It is for the advanced map timing it offers. So far, with the "96 400" fitted, it makes the bike [sound] like a crisper running machine. The '96 400' flywheel's pickup looks to be positioned a little bit further forward in the flywheels rotation in what would seem to provide an earlier pickup signal, (maybe). Other factors may take into account, such as the relation of the timing marks. What is also noticed at a casual glance is that the pickup tab appears to be noticably shorter than the 650Rs pickup which appears it might translate to be a shorter duration. More info. to come when I get the chance to pull my 650s flywheel and make measurements of both.