[Duarte]

Hi everyone i,m writting from Portugal,

So i recently buy my first 2001 400Ex, and i think isn´t properly jetting.

It starts fine with the choke off but after like 20sec goes off

When is warm the idle is fine, but it seem to me that the headers stay hot very quick

When im in a downhill and don´t hit the throttle i have back fire

Im runing with the stock motor air filter lid UNI filter and a FMF pipe only

I search at google Earth and i belive that i live at 1000 feet

i don´t see yet what ar the size of the jets,

I like to have some help on the jets sizes and the needle.
Thank you :wink

 

[Austin92]

I’d leave the needle stock for now. Try a 155 main and see if it’s still back firing or starts bogging or smoking black like the choke is on. Jetting is a lot of trial and error. Google “400EX plug chop”


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[SlammedRanger]

42 pilot jet. And a 155-160 main jet. Mixture screw around 2 1/4 to 2 1/2 out from light seat. And you can drop the clip one slot if you want some more mid power. You may have to go 152 for main if you do that though. Popping on decel is gunna be alot from the stock size pilot. But main jet being lean wont help either

Welcome to the forums!

 

[Goober]

Welcome
Do you have a service manual? I don’t know anything about this model but i will post some listings for a service manual.
I would say that you could take the carb off, remove the bowl and see if there are blockages in the jets.