I just got an 03 YZ450F and need to calm it down a bit for my taste, I race MX in Vet Class. I've read about the flywheel wieghts and think that is my best route, but I have also read about the sprocket combos. What has been everyones best results/opinions? Also what is the most cost effective flywheel weight and where can I get them. Thanks.

Steahly 10oz is the ticket. Stock gearing is actually pretty good. 50t on the rear for tighter tracks. Quiet core exhaust tame it further but may affect your starts. Some like 0ne tooth bigger in the front for taller gearing which makes sense for more open tracks.

Suspension is key and if your not heavy try lighter springs and or a revalve. I'm 170lbs and stock was stiff on the chop for me.

I sold the bike, but missed it and picking up a fresh 03 for $3900 with the 10oz Flywheel, FMF bars. Still had a triple and other goodies around from my first one.

Plan on getting some good starts!

Anyone shopping for a CRF250X? 300 miles!


A flywheel is your best option. I have a 12oz on my 426 and it sure did the trick. I ride the vet class and trail ride and it makes it so much smoother.

Dang! 10 and 12 oz. for motocross?! I'd go with at most an 8 oz. from Duback racing, and gear your rear sprocket up to a 47 tooth. That will totally make your Yammie feel like a smoothe CRF.

10 oz. bolt on from Steahly and the 47t rear sprocket made my '03 great for MX. Still pulls real hard but smooth and tractable.

You could change the front sproket out to a 15t. That helps quite a bit. I dont know how much you want to spend but actually putting on a different muffler mellows it out too. The stocker is really violent. I run a full Ti4 system on mine with the 6oz flywheel and stock gearing and my bike pulls exactly the same as my buddies 04 CRF with a Factory 4 system.

Fox369 for MX run a 4oz Dubach or 5oz GYTR - flywheel weight on the 450. anything over 8oz is too much and is good for woods riding!

Also you can go from 48tooth rear to a 47 tooth rear - this combo will be your best bet to get used to the "Beast", then you can experiment

I tell you what, no flywheel get a Rekluse Zstart auto clutch. You want it to calm down and then have power when you want

Rekluse Zstart Auto Clutch

This one little item will make your bike a completely manageable beast.

Best part is you have a 30 day money back Guarantee from Zstart :thumbsup:

Zstart Web Page

I have the Dr.D exhaust and the 8oz flywheel weight on my bike and that helped. I should have let you take it for spin at Mosier on Monday.


I used a 6oz flywheel weight from GYT-R (Dubach is the same), 2 base gaskets (this was the bigest improvement), Yosh pipe and stock gearing. We tried all sorts of combinations, from changing cam timing to gearing and this worked this best. The stock '04 is extremely better than the '03 but this combination worked well on my '03.

A Flywheel weight is your best bet. Remember when comparing them that flywheels like the Dubach (Dr.D) and the GYT-R will be lighter than bolt-on types because all of the weight is placed on the outside diameter of the original flywheel, where it is most effective. Thus, a 6oz Dr.D is equivalent to a 10oz or heavier bolt-on. As far as semi-auto clutches are concerned, my opinion is that they are for people who don't like four-strokes. I love engine braking. If it's too much you can just roll the throttle back on a little.

Flywheel will help tame it and prevent stalling issues. If theres not stalling issues, try the 15T spocket first. This helped the most on my set up. (My ride, 15T/47 & 4oz Dr. D) I like another responce/post the Best. (GET IN SHAPE)

I am telling you Zstart :thumbsup:

I would go with the GYT-R flywheel ($90 and you keep your stocker) and ask your dealer for a 2005 piston, since they dropped the compression to make it easier to ride. I found that when going with taller gearing, the bike seemed to stall even easier than stock. Another option is the Vortex X10 CDI. You can pick from 10 maps, some are more tame than stock.

1) 6 oz Dubach flywheel weight

2) Un-plug your TPS (throttle position sensor)

3) play with gearing ... i've run a 47 and liked it ... but am now running a 52 because of mostly riding tracks .. 47 makes 2nd gear really useable ... 52 allows me to ride most of the tracks in 3rd gear.

Thanks, guys, your comments were exactly what I was thinking, just wanted to make sure. I appreciate all the input. I'll go with a 6 or 8 oz flywheel weight and stock gearing.

DPW, I should have asked you what all you had done to yours and rode it, but I didn't think about it, too busy worrying about getting used to my beast, oh well get ya next time.

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