Here is what I would suggest as this is what I did with my 04 when I got it... Install a Stealthy Flywheel weight (13oz), cost was about a $100. Make the gearing 14-51. A tapered head pipe if you can find one (I can't remember who the mfg was that I got mine from), run Water Wetter or a good coolant product or addative and stuff a radiator cap with a 1.5 bar pressuer rating instead of the 1.1 bar that comes with it. (I think I stole one from a KTM as it fit and ran a higher rating) and make a small puck jug for the overflow, it doesn't need to be much bigger than about 6-8oz in size and can be easily mounted with the overflow tube run into it (don't forget to vent it with a small pin hole). I rode mine in just about every condition imaginable and the only time I had an issue was in 90 plus weather and having to be just off idle in 1st for a couple miles. It would dump a little bit of coolant, but that was what the puck tank was for.... The flywheel weigth will mellow the nasty hit down and turn it into a pretty amazing traction monster, the 51 toth made first a little lower which helps in the low speed stuff and it didn't take a huge amount of the top, I would say it dropped 6-8 miles an hour off top speed, but the stock bike top speed was in the upper 70s anyway so not a big issue unless you are ricky racer and like to go as fast as you can on open fire roads.... Thanks for the suggestions and everything. Is there any chance you could take a picture of your overflow tank, I am just interested in what yours looks like. I've had my 03 yz450 for two years now and finally have it to where it's great for trail-riding/singletrack. In stock form it is way too tall for the tight woods. I added the 8oz DrD FWW first and that helped some, but the biggest help for me was going 13/52 on the sprockets. I've also added the Clarke tank, lowered the stock pegs, higher bars, Pirelli MT43 and a WR 18" wheel in the rear, handguards, the zipty APS and a kickstand and I'm loving it. I contemplated going to the rekluse or the wr450 gears, but after gearing down the sprockets I'm right where I need to be. Not to mention how much cheaper it was! APS? Accelerator Pump? Was kind of iffy on that acronym. Yeah, I think I am going to put a heavy flywheel weight in and change the sprokets to 13/52 or 14/51. It might already have different sprokets, according to the ad. I am just very excited to see this bike on Sunday, and hopefully get it. I got big plans, but not a lot of money right now, so hopefully I can get it to my single track riding needs without a lot of money at first, will be my project, to set up a bike for me... Which means a lot of suspension work, and springs do not come cheap.