400EX Jetting Questions

[GA400ex]

I am running a White Brothers E-Series slipon with 12 discs, a K&N with outerwear, and no airbox lid on my 2004 400EX. I ride in middle Georgia and the elevation is around see level. Is anyone running the same setup? What are your jet sizes? What position do you have the main set at? Thanks for any help.

[zephead400ex]

Welcome to the site.

I at around 300 ft. I would try at least a 42 pilot, 155-158 main, drop the clip 1 notch. Good place to start.

later

[Sportrax10]

Originally posted by zephead400ex
Welcome to the site.

I at around 300 ft. I would try at least a 42 pilot, 155-158 main, drop the clip 1 notch. Good place to start.

later
So your saying the second position? What will that change?

[GA400ex]

If it is in the second postion, it raises the jet up. This will make the setting richer. The air filter allows more air in, so this will add more fuel to the mixture.

[cals400ex]

wow, we are confusing people, including myself. the mainjet skrews into the needle jet holder. besides that, there is no adjustment for the mainjet. if you happened to remove the needle jet holder on accident you need to skrew it in and tighten the lock nut down so you can see about 3 threads on the needle jet holder. if you skrew this in much farther, you will be hurting the performance. i guess it is because when you skrew this in farther you are actually raising the mainjet because the carb sits on the bike up side down from how you work on it. is that clear?

when you talk about adjusting a jet up or down. you are usually referring about the jet needle (needle). i would probally drop the clip on the needle one position with your mods. the stock clip position is the 3rd and dropping the clip one position is in the 4th when counting from the top. dropping the clip actually raises the needle making your air/fuel ratio richer from about 1/8 to 3/4 throttle.

if you have your stock pilot jet in, you might consider going to a 40 or 42 pilot. if not, i would turn your fuel skrew on the bottom of the carb out 2.5-3 turns from lightly seated and go from there.


it is tough to pick out your mainjet without knowing the temp outside. with your mods i would run approximately a 155-158 main in the summer and a 158 to 160 in the winter. these are just guesses. jetting trial and error and yes it takes time.

[Mikey]

I have basically the same set up as you. Cals400ex recommended 155 main, 42 pilot and needle in the fourth position. It is a huge improvement over stock jetting. No more hard start when cold, popping on decelleration or poor throttle response. I live in Cali, where it is always warm and ride between sea level and 3000 feet. Set the pilot screw at 2.5 turns to start.
Hey Cals, did you get the washer installed on the needle yet?

[cals400ex]

Originally posted by Mikey
I have basically the same set up as you. Cals400ex recommended 155 main, 42 pilot and needle in the fourth position. It is a huge improvement over stock jetting. No more hard start when cold, popping on decelleration or poor throttle response. I live in Cali, where it is always warm and ride between sea level and 3000 feet. Set the pilot screw at 2.5 turns to start.
Hey Cals, did you get the washer installed on the needle yet?

no i sure didn't. i sent a note to c&d when i sent my magnetic drain plug back to them and i asked them if they would send the washer to me when they sent me back the correct plug. well, they still haven't heard back from the drain plug company. so by now they may have forgot about the washer too. if they don't send it i probally won't worry about it because i think i may just get an fcr this summer. i won't need the washer until the warmer months. in the colder months like now, the bike is just fine in the 4th position.

cal