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jcburni

2003 yz450 jetting problems

5 posts in this topic

I've owned this bike for about six months and I am still having trouble with the setup.

Main 165

pilot42

needle 4 from the top

My bike has a full big gun exhaust with the quiet core insert. My elevation is sea level to 5000 and up. I know I can't jet for the large elevation change but most of my riding is between o to 2000.

The bike runs great, it is just on deceleration I am having the problem. It backfires like crazy. Also, is it normal for the bike to die when pushing in the hot start.

I am also wondering if there is a way to tell if I have a jet kit or not. If I don't is it quite easy to install the dj kit. I did the install on my drz and it was a snap. Is the yz just as easy.

Thanks for any help you can provide

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You are going to have to increase the size of that pilot jet. I would jump to a #50 since you have that after market pipe on it and your high elevation.

High elevation and pipe upgrades leans all bikes out. Start with a #48 or #50 and work your way up. I am thinking that a #50 is all you need because I had the same problems with mine and my elevation is 2500ft up to around 5000ft. I installed a #55 jet and set the fuel screw to 1.5 turns and now is runs like a champ. My bike is a 2006 though.

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You are going to have to increase the size of that pilot jet. I would jump to a #50 since you have that after market pipe on it and your high elevation.

High elevation and pipe upgrades leans all bikes out. Start with a #48 or #50 and work your way up. I am thinking that a #50 is all you need because I had the same problems with mine and my elevation is 2500ft up to around 5000ft. I installed a #55 jet and set the fuel screw to 1.5 turns and now is runs like a champ. My bike is a 2006 though.

Quite the opposite, if I may say. The higher the elevation, the smaller pilot you have to go. Larger pilot jet increases gas ratio in fuel (=gas + oxygen) and what do you do with more gas when the oxygen levels drop in higher elevations? Less gas when there is less oxygen.

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Right you are, Roger. Higher elevations and higher temps both reduce air density, and both therefore require leaner jetting to compensate.

Go to the page I referenced and find someone with an '03-'04 jetted for 3500 feet and start there. I almost never tweak the jetting on mine, and I run it from below sea level (yes, really) to 3500 feet with the same set up. No problems except an occasional tweak of the fuel screw, so you should be able to find something that will work in your range, too.

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