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Scooter426

2004 YZ450 Jetting

9 posts in this topic

I just got a 2004 450 and need help with the jetting setup.

It is basically stock. I live at sea level in Seattle, and am experiencing 1/8 throttle surging. It seems to run fine everywhere else, but the fuel screw seems to have no effect on the problem. Please let me know what settings work for a basically stock setup. it does have a flywheel weight and I changed the air filter to an aftermarket one (No change in the problem). Pipe is stock 2004. I am guess it is lean surging, I have heard these bikes are lean as delivered.

TIA,

Scott :cry:

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Try going up one pilot jet size at a time and make sure the end of the fuel screw hasn't been broken off in the hole. I know some of the aftermarket screws have a bad habit of breaking off if you seat them too tighly.

If its stock, it should have a 42 in it, try a 45.

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I richened the pilot to a 45 and leaned the needle by 1 clip position, i know seems strange but this cured the surging when the throttle was at a constant position between 1/4 and 3/4 open. The larger pilot gives real good throttle response off idle

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so stock settings are

pilot: 42

Main: 165

???

and I should change to:

pilot: 45

main: 168

sounds like the aftermarket fuel screw is a good idea, also.

Are there any differences in the 2003 and the 2004 in the Carb/Jetting/Engine settings?

thx,

scooter

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That's what I went with. I also raised the needle one clip to richen the mid a little. The bike runs great but does surge a little at half throttle. I'm thinking the cool air will cure that soon enough though. I don't think I'll mess with the needle any.

I'll probably drop the 170 MJ in when it cools off.

As for the Zipty fuel screw, I love mine. It's worth its weight in gold.

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found a 45 pilot and a 168 main in the ole' tool box. I will change the two asap and let you know how it goes. And I will but the needle one clip richer(down).

-scooter

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I couldnt find a better thread to throw this in...

I just put the new cdi unit in. It is without doubt where they killed most of the low rpm power at. If you are one that likes a hit when you pin the throttle, Just swap out the cdi. :cry:

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My 03 runs like it is lean at 1/8 throttle I can't make it stop i even put another carb on it. and it does that same thing at that rpm :cry: It run's great It just sounds bad at that rpm I think it's a CDI thing :cry:

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