got a "new" 03 yz450, many questions

3 replies to this topic
  • hammer940

Posted February 18, 2007 - 09:59 AM


I'm new to the thread and was hoping you guys could help. I bought a 03 yz450. Its my first 4 stroke and I'm looking to get back into racing after a long absence. It will be about 50% track and trail. What do I do about the tall first gear? How should I change the gearing so 1st isint so wide and stalls so easily on tight nasty trails? It has ti FMF powerbomb with Ti4 muffler. It pops really bad (loud) when engine braking. Is this normal or a jetting problem. Supposedly the dealer I bought it from checked the valves. How reliable are these motors? And finally, where online can I get a printable manual? Ive looked and looked, and dont have the money to buy one.
Thanks ahead of time, and man these things rip!!!!!!!

  • Jaycycle

Posted February 18, 2007 - 10:04 AM


1. A flywheel weight is highly recommended with the 03's. It will help greatly with staling in 1st.

2. Its a jetting problem, its running lean. Someone else can help you from there.

3. These motors are pretty tuff. I think you will be pleased.

4. Not sure... But I'll look.

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  • Jaycycle

Posted February 18, 2007 - 10:09 AM


Try this... http://www.yamaha-mo...3&lid=2&mid=166

  • flintlock28

Posted February 18, 2007 - 12:24 PM


The 03' is virtually bulletproof, if you change the oil/oil filter religiously, and keep the air filter clean.

As Jay wrote, the addition of a flywheel will help with trail riding in the tight stuff. Unfortunately, the 4 speed isn't as versatile for trail and track as a 5 speed, because if you gear it down for the tight stuff, than you will lose some of your top speed capability if you ride long wide open areas, or high speed fire roads. I have the 04' model which is basically the same, and I 've learned to live with the gearing....and I've gotten so good with using the clutch, that stalling is a rarity anymore in the tight stuff.....just get a 8 oz. or so heavier flywheel to help with stalling. You can also turn up the idle a bit when riding the tight stuff as a type of "poor man's" solution to stalling (it does help a lot)

If I were going to ride a lot of tight stuff, and didn't ride a lot of wide open/high speed areas, than I'd think of maybe adding two or three teeth to the rear sprocket..stock is 48 teeth, you could maybe go with a 51 tooth model.

About the popping, since it's gotten colder, you are probably running lean and need to adjust the Fuel a search about it, and try turning it out to make it richer about a 1/4 of a turn (at a time) until popping is only occasional on de-celerration....a little pop on decel is normal, you just don't want it sounding like a machine gun.

As far as the manual goes...they run about $ 60 from the dealer. I got one brand new off of @bay for $ is an excellent manual (Regular Yamaha service manual)..there are also the same manual's on @bay on CD-Rom's for about $5 or $ 10, but I like having a physical book in front of me.

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