I really like my '06 YZ450 but it took a lot of time and work to make it a really fun bike for the kind of off-road mixed desert/woods riding that I do. One of the problems I've been wrestling with for a couple of years is the rear shock. I've revalved it a couple of times and it works pretty damn good if I am riding the bike aggresively and have my weight on the bike correctly, but it's not very forgiving if I have a surprise hit or if I'm too far forward on the bike in breaking bumps/not on the throttle hard. In other words, I have to ride it like I'm racing all of the time.... not for leisurely riding. I've known what the problem is for quite some time (too much high speed compression damping) but no ammount of swapping shims on the compression stack would help (even did some porting on the piston). I could get improvemnts in the HSC, but changing the stack too much would always lead to a compromise somewhere else....until I figured this out! In '06, the YZ's went to an 18mm shock shaft. For eons before '06 they were 16mm and the WR remain 16mm, even today. I recently had an '02 WR shock (16mm shaft) apart and noticed the HS compression adjuster had 8-2mm hiles in the end plate. I also had a shock for an '05 YZ (16mm shaft) apart and looked at it, it had 6-2mm holes. I also had another stock '06 YZ shock (18mm shaft). When I pulled the compression adjuster out and apart of the '06 shock, I compared it to the '05 and they were identical in every dimension. The only difference was the color of the anodizing on the HS adjuster nut. Hmmmm....... So, I decided to do a little experimenting. I took my spare '06 compression adjuster apart and drilled the six holes from 2mm to 3.8mm (#25 drill bit). About the biggest I could go without encroaching on any sealing surface. I reassembled it and swapped it with the one on my bike. The cool thing about making mods to the compression adjuster is you can remove and replace it without pulling the shock from the bike. Just lay the bike over at about a 45 degree angle on a stand, empty the N2 bladder, and unscrew the adjuster. If you have the bike at the right angle, you wont introduce any air into the shock. After I put the modified adjuster in and recharged the shock to 145 psi, I went for a spin. WOW! what a HUGE difference on sharp hits! I could blast down a gnarly jeep road littered with grapefruit sized rocks and rain ruts while I was pinned in 4th gear and sit on the seat like I was in my recliner! It worked great but with a price. The high speed adjuster had no effective differece if it was fully out, or in 2 turns. Back to the drawing board. I pulled it apart again and did a little research. SDI sells a lighter HS compression adjuster spring with a special washer/seat (Factory Connection sells one too, but it's only the spring). I have used the Factory Connection spring and didn't notice much difference. The stock spring seat sits on the clamping shim. The special spring seat sold by SDI has a relief and alows the seat to sit on the outside edge of the HS adjuster shim stack. I made my own spring seat like the one SDI sells and assembled it with the light weight FC spring. I also did another small mod to the shaft that would allow 3 full turns on the HS compression adjuster. Back together and recharge the shock again. This time on the check ride I had all of the adjustability I could ever want AND I finally have fixed the problem of too much high speed compression damping. All for under $50! The WR orifice plate vs. the YZ HS compression spring with the modified spring seat. Adjuster assembly. The spring seat, shaft, and orifice plate are on the right.