Here is my list of the mods needed to make your WR450 run properly. It focuses on the 2005 model but most is applicable to all 450 models. Any corrections, comments, clarifications etc are welcome. I hope that one of the mods will make this a sticky at some point. 1: Throttle Stop: When your US spec bike arrives, there is a screw that prevents the throttle from opening fully. You either need to cut it down so that there is 18.23mm of thread (not including the head), or order yourself a YZ450F throttle stop, part no 5JG-14591-00. Canadian, OZ and European spec bikes come with YZ throttle stops and do not have this problem. Do not simply remove the throttle stop, as this will cause your throttle to function improperly and can damage your engine. 2: Exhaust baffle: This is not required if you are going to add an aftermarket silencer. The stock exhaust baffle greatly restricts the bike, reducing power. Removing this baffle will increase the power, but will drastically increase the noise levels. If you are using the bike on closed MX courses or private land in a remote location, this should be fine, it's not going to be louder than any of the 4 stroke MX bikes out there. Removing the exhaust baffle requires removing the end cap from the silencer, taking the baffle out, and putting the end cap back on. On 2004 and earlier bikes if you are using the bike on public land or are concerned about noise you can either pick up a quiet exhaust insert for your stock silencer from www.promotobillet.com, www.quietiscool.com or get a GYT-R one from Yamaha. These aftermarket baffles will not work on the 2005's, but ProMotoBillet will have an insert for the '05's available next month. 3: Grey wire: With the exhaust opened up and full throttle range achieved, the ignition needs to be changed to YZ specs. Like the throttle stop, this only applies to US spec bikes. To change to YZ specs, you need to follow the instructions here: http://www.thumperfaq.com/gray_wire.htm 4: Removal of AIS: The '05 WR450F (but not the 250) is califronia green sticker legal. In order to achieve this, yamaha had to install a smog pump, also known as a bunch of goofy pipes that get in the way. This can cause lean jetting and backfire. There are two ways to remove this. 1) order the kit from TT member 'Lowedog' or plug up the holes with rubber plugs. This is discussed in this thread: http://www.thumpertalk.com/forum/sh...ad.php?t=206843 5: Chain slider: When grit gets in the space between your swingarm and the chain slider, it rubs into the swingarm and can eventually wear a hole in it. This is easily fixed using some silicone sealant as described by the late, great motoman393 here: http://motoman393.thumpertalk.com/tech/swingarm.html 6: Jetting: In stock form the bike is fairly lean. Once you free it up, it is REALLY lean. If your bike comes with spare jets, see if any are suitable for your weather and altitude. If not, either order appropriate jets or get the JD jet kit (available from thumpertalk). A little rich is better than a little lean. 7: Remove air box snorkel: US versions have an airbox snorkle behind the battery. Take it out. 8: Fuel screw: This is more optional than the other mods, but some people consider it to be necessary. Zip-ty makes the most popular fuel screw and it is described here: http://www.ziptyracing.com/display/...&CategoryID=110 Scotts performance, koubalink and MSR also make equivalent products. Additional Notes: Note 1: Oil choice and break in method are controversial subjects with many threads and no conclusions and will not be discussed here. Note 2: Your electric start may not seem powerful enough. Once your engine breaks in and you have done some miles it will work much better. It may not ever work well on a cold engine in cold weather, but that is the price you pay for a relatively light e-starter.