400ex Jetting PLEASE READ

[cmdr]

Ok, I have a...
1999 Honda 400ex
White Brothers E-Series Slip-On
Stock head pipe
K&N Air Filter
Outerwears Pre-Filter
Stock Airbox and Stock Lid ON

My location is as follows...
Currently 65-90 degrees in the summer about 80% humidity and an elevation of 1378 ft.

The type of riding I do is hard/fast-paced trail riding, I usually ride with other 4x4's and ocasionally go through seat height mud/water, that being the reason I can't modify my airbox. I am not sure what my current jets are but I do know that the previous owner had stock exhaust and the K&N air filter and outerwears with a stock airbox and stock lid on and he rode at mountain elevations and modified the jets. So I'm assuming he put smaller jets in, and at my elevation I can deffinately feel constant back-fire when the machine is cold and doesn't idle at all when cold.

I plan to buy a jet kit from www.jetsrus.com, I would like to have a general idea of what jets to put in to start with and needle position. I haven't installed the pipe yet so I'm not sure how many plates I will be using but I will probably have all 12 installed.

Thanks alot for your help.

[Crazy400EX]

uhhh maybe 42 pilot.........160 or up main.

[cmdr]

Thanks for the quick reply, ya I was thinking something like that for a main jet, the jet kit I'm getting doesn't include any pilot jets is that gonna be a problem? Isn't the pilot jet really only for idling?

[Crazy400EX]

ya that and whn you get on the throttle quick.

[cals400ex]

forget the jet kit. buy individual keihin jets. you should be able to get them from your local dealer or C&D racing can also get them. i would get a keihin 155 mainjet. run the stock keihin B44A needle in the 3rd clip position from the top. run a kehin 42 pilot jet. start at 2.5 turns out from lightly seated on the fuel screw

if you run a jet kit, all of this will change besides the pilot jet and the fuel screw. the mainjets are measured differently so a 155 keihin will NOT be the same as a 155 dynojet (mainjets in the kit). also, you will get a different needle too. thus, the clip position may be different.

i would get the individual keihin jets that i mentioned earlier. if your dealer is lost you have two options:

1: tell them the mainjet you need is a 13 series. tell them the pilot jet you need is a 21 series. that should help answer questions

2: order them from C&D because they know what you need

[Crazy400EX]

i knew that HAHA


Listen to cals, hes way smarter than me!

[cmdr]

thnx cals I'll probably go that way but the jets in the jet kit i plan on buying are original keihin jets exactly like stock, and im not sure what size jet im gonna need i think that a 155 would be too small for my setup and elevation i was thinking 160 range

[cals400ex]

Originally posted by cmdr
thnx cals I'll probably go that way but the jets in the jet kit i plan on buying are original keihin jets exactly like stock, and im not sure what size jet im gonna need i think that a 155 would be too small for my setup and elevation i was thinking 160 range


if you think that is too small, that is fine. we actually ran a keihin 152 with the same exact mods as you, AND we are at lower elevation levels than you. lower elevation means more avaliable oxygen in the air. you would be fine with a 160 if you want to run that, the bike will run just fine. you just won't have quite as much speed up top. if you do a search most people actually run a 152 or 155. some prefer a little bigger, which is fine. just pick up a few jets if you want. pick up like a 155, 158, and a 160. that or whatever you think suites you best. good luck :)

[cals400ex]

Originally posted by Crazy400EX
i knew that HAHA


Listen to cals, hes way smarter than me!



hey you were on the same track as i was. no one said i was any smarter than you are. ;)

[Crazy400EX]

haha thanks, its just one of those things everyone know........your normally the one who helps me with all my problems!

[sickmojave]

Originally posted by Crazy400EX
........your normally the one who helps me with all my problems!

I agree.. Most of what I know about jetting I learned from reading cals post.....;) :D