Exhaust Jetting on 400ex

[yellowWB400ex]

I bought a R4 full system and I need to rejet it but dont know what to run. I run it with stock air filter and with lid on and off depending on how I feel and what I am doing. I know nothing about this (pilot & main jets and how to have the screw). PLEASE HELP!!!!!:confused:

[plkmonster2]

If you could, post your elevation, and temps please! FOr what you show now, A 158 main, 42 pilot, fuel screw 2-2.5 turns out should suit you well with the lid off. A 152-155 main if you run with the lid on. Also, a Uni filter would help you gain more out of that pipe. ;)

[yellowWB400ex]

I live in Upper Wisconsin and so anywheres from 20-75 degrees. If that helps. I have a dyno jet jet kit 1 & 2. I want to make this easy and use as many stock things as possible. Try not to be too complicated.

[yellowWB400ex]

can anybody else help me with this

[cals400ex]

dynojets are NOT the same as keihin jets. i would just put in the dynojet 155 mainjet. remember, there is an adaptor with that mainjet if you have the dynojet kit. the mainjet goes in the bottom of the carb while the needle goes in the top. actually, look in the frequently asked question forum on this site and it shows you how to install this under "K&N power kit."

[yellowWB400ex]

so i should get keihin jets instead of the dyno jet kit. Just use the 155 with and without the lid.

[cals400ex]

you really need to rejet with and without the lid. if you already have the kit, i would use it. if you don't, i wouldn't buy one. with a dynojet 155, you will be fine with an without the lid. however, with the lid on your either going to be a tad rich or with the lid off your going to be lean if you don't rejet. a 155 dynojet should be fine either way but will run a little better with the lid off probably because your jetting will be a tad leaner.

[sam the brave]

i think a 155 main will be tp small
i have a 160 in mine and its stock with air box removed

[RIDER11X]

Rejet without the lid. At worst you will be too rich with the lid on. You don't want to go lean, or damge could result.:eek:

[cals400ex]

everyone's idea of rich and lean is different. one person will say my jetting is too lean and others say they would go smaller. i jet my bikes probably a tad leaner than most, but then again i go by feel and sound on my bikes. good luck

the bike will probably run just fine whether you run a 146 dynojet or a 170 dynojet. a 155 dynojet is larger than a 155 keihin. removing the air box lid changed my jetting up to 2 mainjet sizes on average. with your set up at 625 feet above sea leve in 70 degree weather, i would run a kehin 158 at largest. some would rather run larger, some would run smaller.