08 450 fuel mixture screw

Hi, I fairly new with 4 strokes I've owned a few but usually kept them stock and just changed oil and had valves checked.

I just bought a 08 yz450 and it had a dr d exhaust that had a cracked in it so I replaced it with a full fmf 4n1 exhaust with the power bomb header.

It has a fuel mixture screw on the bottom of the carb with 1-2-3-4 on it, when I warmed it up and rode it down the rode and back it idles and runs great but at an idle if I "somewhat" chop the throttle it dies, I don't think I was fully up to operating temperture but I wanted to see what i should be looking for tomorrow for signs of being to lean or rich while riding? and what adjustment to make. It was tuned for the dr d full sytem previously (fyi)

Im not sure what the 1-4 stands for as far as clockwise-lean counter-rich??......

During riding it seemed like it did it a few times as I would brake for corners and accelerate it would sometimes stall. i don't have much experience on a 450 more on the 250f so the power difference is what im getting used to and I could drive hard into the corners and power out so the motor never really idled into the corner where as now I am hahaha.

Any info and tips would be great and appreciated :ride:

And the aluminum aftermarket fuel screws are more than likely JUNK. I bought a PC one and it wasn't even machined to the same size as the stocker...

And the aluminum aftermarket fuel screws are more than likely JUNK. I bought a PC one and it wasn't even machined to the same size as the stocker...

I have a moose racing (made by zip ty) screw and its kick a**. It fit perfect, has a heavier spring than stock and has never backed off under vibration. Have had it for a year.

And the aluminum aftermarket fuel screws are more than likely JUNK. I bought a PC one and it wasn't even machined to the same size as the stocker...

my wb work just fine. u better get a band to hold it in place tho, beacuse it can vaibrate it self lose, i actully found mine on the crankshaft case ones, the band fixet it.

i have few friends that use aftermarket cheap aluminium fuel screws and none had a problem.

i dont think you supposed/need to chop the throttle on a 450.

you can try to rise the idle abit maybe, clean the air filter, adjust carb.......

my 06 will die to if i chop the throttle like a 2 strokes.

use the search engine you will find what you need.

The question no one has answered is that the numbers are simply there as a visual reference to help you see whether you've turned the screw a full turn, half turn, etc. The screw meters an air fuel emulsion, so it's richer as you turn out, leaner in.

The link to Eddie's post is a good one, but skims over the basics a little quickly. Keep it in mind though, and read this:

http://www.thumperfaq.com/jetting.htm#PJ

thanks for all the input it really helps!

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