Changing Jets???

[mxva5413]

What's the easiest way to change the Jets on a 400ex (just the main jet).......What I mean is do you actually have to take the whole carb out of the frame or can you kind of turn it like I do on my KFX 400? Also what jets would you recommend for a FMF Power core slip on and UNI filter with lid removed?

[cals400ex]

to change the mainjet:

turn the fuel off. remove 17mm skrew on bottom of carb. remove mainjet with 6mm socket. put new mainjet in with 6mm socket, but don't tighten really tight. put 17mm screw back on. turn fuel on and go.

no plastic needs to be removed for just changing the mainjet. good luck

[mxva5413]

Thanx that took all of about 5 min lol.....It's much easier on the 400ex than the z400....well after you know what to do :) Thanx again! I bought this bike used and the guy told me it had been jetted I just wanted to make sure.....going racing tonight and wanted it to run the best it can....so far it's got a 148 MJ I was thinking about going by the Honda dealer and getting atleast a 155 and trying that?

[04'400ex'er]

Originally posted by mxva5413
Thanx that took all of about 5 min lol.....It's much easier on the 400ex than the z400....well after you know what to do :) Thanx again! I bought this bike used and the guy told me it had been jetted I just wanted to make sure.....going racing tonight and wanted it to run the best it can....so far it's got a 148 MJ I was thinking about going by the Honda dealer and getting atleast a 155 and trying that? If you have no mods to your motor yet, no need to jet. It will just run chitty from being too rich. With the pipe and filter, I would start at 155 main, working your way up till you have the right size jet. Cals knows ALOT more about this stuff than I do, though.

[cals400ex]

yeah, what mods are done to the bike? air box lid on or off? what elevation and temperatures do you ride in? the stock jetting in a 400ex is:

148 MJ
3rd clip position on needle
38 pilot jet
2.25 turns out from lightly seated on the fuel screw


usually a 155 MJ is good for a piped and filtered 400ex. however, like i mentioned earlier the temperature, elevation, humidity, air box lid on or off, etc. all matters.

[mxva5413]

No it's not stock well the motor is but it does have a FMF Power Core 4 slip on and UNI airfilter and air box lid off for racing.

[Cole Trane]

If you go to the dealer, make sure you get an aftermarket jet and no a stock one. The stock jets cost about 15 bucks a piece!!

[cals400ex]

yeah, basically you may be able to buy honda or keihin jets. they are the same thing and the keihins will cost less because on the package it doesn't say honda. a 152 or 155 sounds good for your mods.

[hondarider2006]

Originally posted by 400exrider2002
If you go to the dealer, make sure you get an aftermarket jet and no a stock one. The stock jets cost about 15 bucks a piece!!

Get them from C&D for $3 a piece;)

[mxva5413]

Originally posted by hondarider2006
Get them from C&D for $3 a piece;)

Only problem is I needed them last night LOL....So i went to Honda House and they cost like $7.50 each I bought a 155 and 160 ran 155 last night with the stock airfilter cause I left the UNI at home on my bed LOL!

[OregonEXrider]

I have pretty much those same mods and a 158 was a little to lean, so I popped in a 162 and now it runs like a raped ape!:D MY elevation is sea level though.....

[mxva5413]

Originally posted by OregonEXrider
runs like a raped ape!

LMAO