Jetting my 03' 400EX w/aftermarket pipe?

[rohlik125]

I want to change the jetting on my 03' 400EX. I just bought a White bros. E series slip on from a guy and he said it would be best to rejet. I also just installed a TwinAir air filter. I know I read something about this on here before, can anyone send me in the right direction? Thanks.

Aaron

[400eXr1d3rZ]

What's your elevation, average tempature, and tempature now?

155 main, 42 pilot, 2.5 turns out fuel screw, needle on 3rd clip from top. That should be a good starting point.

EDIT: Once you change your pilot you don't need to change it again, less you do a stroker kit with a big bore or something, a 42 pilot is good, it also cures the cold starting problem. When I had a white bros. slip-on and twin-air filter (and no other mods) i had a 155 main and 42 pilot, 2.5 turns out fuel screw and needle on 3rd clip, worked perfect! that jetting is good to about below sea level (around 25 or so) and to about 3000. But you have to rejet for different tempatures. If it's cold you need to go richer, more fuel, and if it's hot you need to go leaner, more air less fuel.

[rohlik125]

Hey thanks that pretty much answered all my Q's. I live in Minnesota so it gets kinda cold in the winters, but also pretty warm in the summers. Max cold riding would be from 0 to 20 above zero, and Max hot riding temp for me would be around 90. Thanks again. Oh yeah, would you recomend any jet kits that are out there?

Aaron

[hornetgod13]

www.jetsrus.com
They carry all the assorted main and pilot jets you may need. I would recommend buying the steel allen screws they sell to replace the 4 soft metal screws on the bottom of the carb that strip out.
If you remove the air box lid I would bump it up to a 160K.

[rohlik125]

I heard of guys doing this, does it really help? It seams like you would get a lot more dirt and dust in there.

[400eXr1d3rZ]

Originally posted by rohlik125
I heard of guys doing this, does it really help? It seams like you would get a lot more dirt and dust in there.

Doing what?

[rohlik125]

O sorry, I was talking about guys removing there air box covers and the advantages. And one more Question, you said to rejet for temp changes, how much do you change in jetting for temp changes? Like if I get a 42 pilot jet, what size do you get for colder and for warmer temps. Thanks,

Aaron

[hornetgod13]

I have my stock air box lid removed and I installed a EHS Racing Lid. It has large hole cut in the lid and Outwears covering it to keep mud and large debris out. It opens up the airflow and still provides a measure of protection from water intrustion.
Temperature changes effect jetting. If it's cold outside drop your jetting down one size I.E. 155K to 152K or 160K to 158K. The "K" stand for the brand Keihin. Stock jets are 38K Pilot Jet and 148K Main Jet. The stock fuel screw setting is 2 and a 1/4 out from lightly seated. There are many different manufacturers and the numbers and sizes vary. I suggest staying with stock Keihin so they are easier to track and you don't get confused. A DynoJet 160 and a Keihin 160 are different in size and you'll have different results if installed.
If you install a 42K Pilot Jet with the fuel screw set at 2 to 3 turns out from lightly seated you will not have to change it with the changes in temperature. All you will need to do is turn your fuel screw out a 1/4 turn to full turn in the Winter. This will richen the idle mixture and in the Summer turn it back in a 1/4 to full turn which lean it back out.
I also run a UNI filter. I have no problem with dirt getting past my filter. The key is to clean and oil the filter often. If you run with the lid off I would highly recommend getting an outerwear protector for your filter. The inside of the air box will get dusty but your filter will take care of the motor. If you run in really rainy or muddy conditions keep your lid on.
Here's a link to the EHS Racing Lids I was telling you about.
http://www.ehsracing.com/products/400ex_airbox_EHS.htm

[rohlik125]

Hey thanks for all your help, thats exactly what i wanted to know. I just ordered some jets from jetsrus.com. Thanks again,

Aaron