Strange jetting problems with 03 YZ450

hi, ive got an 03 450 and its got some very confusing jetting issues. Its a canadian model, in central manitoba. It has a 168 main, 42 pilot, 3rd clip and a twin air filter. Symptoms are popping on decel, hesitation, and a strange motion in 4th gear. Why do the 04's come with a 172 main 45 pilot and 03's with a 165 main 42 pilot? My 2003 manual just says a 165 stock with no alternative for other countries. I noticed in a 2004 manual that canadian models come with a 172 as the US models come with a 165. help please thanks

I'd try going to the 4th needle clip position. You might be a little lean in the midrange.

that bike came with u.s. jetting. it should have had a 172 main & 45 pilot. the very first thing to do is get the correct jetting in place. get a 172 main and a 45 pilot. the sputtering, or cutting out in 4th (when the throttle is held constant) is a lean condition...simply put, the bike doesn't have enough fuel all the time to hold that engine speed. if you crack the throttle from that position, all is well, until you cruise again...that's the accelerator pump helping things out.

1) get the 172 main (buy a 175 just to have around)

2) install the 45 pilot (buy a 48 also)

3) buy the Zip Ty fuel screw

Your bike had a 165 main & 42 pilot, the main was upped to account for a lean condition. It's obvious now that it should have come with a 172 stock, so the 168 (which seemed like a richer jet, is still lean by stock specs).

I have '04 450 north of the 49th and run a 48 pilot, 172 main and may go to 175.

Do these things, ignore what other uninformed TT's tell you and send me a PM.

Vet28 :thumbsup:

hey vet28, any/all replies here are to help our fellow riders. all of us may not be an "expert" :thumbsup: like yourself, but to make a comment about "ignore what other uninformed tt'ers tell you" is offensive. you should apologize to us all. :devil:

well said stroker. :thumbsup:

Do these things, ignore what other uninformed TT's tell you and send me a PM.

Vet28 :thumbsup:

Now that is not very nice! :devil:

OK...let me apologize. I have learned alot from this group and respect most of the input. This TT'er sent an earlier message about bike problems (or what he thought were bike problems). The replies he got were causing no end of trouble to him and me (I sold him the bike). A simple lean condition aqbove 1/2 throttle had replies telling him he had bent shifter forks. All I am trying to do, is to let him know what the problems/conditions are and try to keep him focussed on solving them. He was damn near tearing a motor with 20 hours on it apart, because it was cutting out in 4th (with the throttle held steady above 1/2). Like I said, I do apologize, Vet28 gives love to all TT'ers. Let's all go back to being friends again.


Vet28 :thumbsup::devil:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now