Help me understand this as the more I think it over, I can't understand why Clarke says it won't work. I have a Clarke 3.6 gal tank on my '08 WR450. It's a great tank and thought it would be great for the '06-'09 YZ as well, but Clarke says it does not fit. Why? The IMS 3.1 fits both the YZ and WR as does the the Acerbis 3.3. Seemingly, the way the tank fits around the frame backbone is the same on both bikes for the IMS and Acerbis to fit, so why not the Clarke? I realize that you may have to buy WR shrouds, but other than that, should it not work out? Does the seat fit differently on the YZ than the WR? When I had the IMS tank, my seat fit fine. I know that Clarke has a 3.2 specifically for the YZ, but extra capacity is a beautiful thing sometimes.