'03 YZ450F setup help

Okay all, I've been riding a 2-smoker all my life and just went out a got myself a super clean '03 YZ450f. Of course, I don't know jack about how to keep this thing on the road! I do have a KTM thumper, but admit that it does get much use, at least compared to all-out desert riding like the YZ.

So questions are as follows, any input, guidance, or comments on one or all would be great.


I'll have to admit that I didn't ride my YZ250 last season due to a back injury, and now I'm almost 30lbs heavier. I believe the suspension is stock, what should I look for to get the suspension set up for a 195lb rider? I love working on my own stuff, but realize that sometimes you just get a better result with a pro. Are these changes something I can do, or do I need special tools, etc.?? :cry:


I keep hearing that these valves aren't like the 4-strokes of old (ride 'em forever and forget'em!). Any guidance on how many hours they should be adjusted at? I have the manual and will be reading up on how it's done, but I've seen some better threads on real-world valve adjustment experience, any of that would be great!

Motor mods:

What's out there, is it worth doing?? I've read about the flywheel weight, but have really had a problem slow-speed power and I don't mind the power curve at all. Any Cam changes or Port and Polishing that helps these?? Any good shops that you can recommend? :bonk:

Thanks for your guidance. I only hit the desert for a day to do some riding and hit a few jumps to try everything out, but so far this bike is awesome!

jb :applause:

The stock spring rates are OK for your weight, according to Race Tech, and that's what I run (I'm around 180). The '03 fork seems to like Mobil 1 Synthetic Dexron III ATF as a fluid. A set of sub tanks will help them quite a bit, too. I Built My Own setup, but they can be bought as well. Enzo Suspension does fantastic work on the older Kayabas like these.

Mine has never yet needed a valve adjustment. What happens, though, with Ti valves is that they go for a very long time like that, and then at some point, the hard coating finally wears through, and they start closing the clearance up fairly rapidly. That's the time when you need to do a valve job. The wear progresses quickly from that point, and you may be tempted to try to squeeze another ride out of it, because it will never happen at a convenient time. Don't do it. Once the shim size has gone to .15-.20mm smaller the the original, there is a risk of breaking a valve head off.

Unless you're really in a situation where getting the absolute most out of it is critical, like Super Moto or flat tracking, leave the engine as is. It's as fast as most anything as is, and is as reliable as a 25 pound cast iron doorstop. Mods to make it work better are an FMF PowerBomb header, with or without the rest of their system, and a heavier flywheel. The pipe smooths out the transition from low to midrange, and broadens the whole power curve noticeably. The heavier flywheel makes an '03 much more controllable, and you can rip into it in more places without vaporizing the rear tire. I run an 8 oz Dr.D, and it really helps the bike bite into the dirt instead of flinging it 45 feet. It rolls the tire easily, just not as hard, and it accelerates far better in poor traction than it did. And it DOES NOT make the engine slow or sluggish in any way.

If it has the original clutch, get the GYT-R Clutch Kit and the GYT-R Pressure Plate. These are Hinson parts sold at a lower cost with Yamaha's name on them. The kit includes an updated actuator arm that reduces the pull effort, and together this will make the clutch much smoother.

I also raised the gearing to a 15/49. Makes first a little tall, but the top speed is cool.

Damn, that's what I was looking for!!!!


Great information, and I'm glad to hear that I might not be too far off. Like I said, I only rode one day in pretty wide open, hard pack desert and it wasn't all too bad. I did bottom the front forks more than I'd like, so I might start with a slightly stiffer front spring. I'm going to hit it this weekend and work those settings over again.

As far as motor... both of those seem reasonable. I came across a fella' with a GYTR motor weight that he sold the bike and isn't using, but unfortunately doesn't know the weight. It's a good deal, but not knowing the weight worried me, is there a way to tell?? Like a part number on the weight??

Muchos gracias!


raise the fork oil level to between 110mm and 100mm it makes a massive difference, set mine at 105mm and it is way better -- think stock is about 130 or so. don't worry about messing with the motor, most try to tame it a bit, i like the so called 'hit' so didn't add a flywheel weight but did lose a tooth off the rear sprocket went to a 47 and love it :applause:

Ya, I'm leaning towards little or no motor mods. Defintely going to go down a little in the rear sprocket, then think about the flywheel weight if anything.



I tried a 15/48 yesterday and it was pretty cool. It was a little lacking at the bottom so might go up a tooth in back, but for hardpack desert riding it was great!!

My buddy pulled up side by side on his CRF450 in about second gear and drag raced. I spanked him. I love beating Honda's.



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