strange acceleration with my 400ex

[Warrioreater400ex]

aight, my 2001 400ex has wb e series slip on, k&n filter, and jetting. in 1st or 2nd gear, if i go from 0% and then all of the sudden punch it to 100% throttle, it tries to die, but if i get to bout 10% then punch it to 100%, then it accelerates in awesome speed..... is this normal? or is my jetting done wrong?

[400exRacerX]

if it bogs when you crack the throttle your engine is getting to much gas (rich), what you can do before your pull apart your carb again is you might have possibly over oiled your air filer so strip the oil and re oil with less, if it still bogs then you need to lean it out.

[Warrioreater400ex]

its not the air filter........ so what do i do? does it have something to do with that needle?

[nakomis0]

It does that even after its warmed up?

[Warrioreater400ex]

i dunno, i havent ridden it for over 5 minutes at a time yet, cuz im not "ridin" it yet cuz i still gotta get nerfs and they are pretty much essential, i don wanna risk it w/out them.... but does yours do that when its cold sometimes or something?

[Chef]

i rode for like 2 years without nerfs, i think you can probably handle one ride

[Warrioreater400ex]

i know I can, but my dad just wants me to be on the safe side, and hes payin for the nerfs bumper and the whole 400 ex, so i had no objections hahha

[nakomis0]

Ya I noticed mine do that a few times before it got warmed up, after it was warm no problems. I'm not sure if theres any fine tuning you could do to fix it,

[Warrioreater400ex]

i hope itll work out, cuz i dont wanna be comin out of turns on our mx track and punchin it and it gagging..... that would make me look great!

[4punksdad]

you didn't metion what size jet you switched to. you didn't mention the status of your airbox lid..............and if your bike is cold, throw all tuning out the window.

the 400EX is as cold blooded, or worse, than your 300EX.

I can tell you that my 400 has NO flatspot.............

[Guy400]

I've owned a '93 KX250, 3 LT250R's, 2 LT230S's and a Raptor. Started riding the LT's when I was 12 and in the 13 years of my riding none of my bikes have had nerfs. I've never had a problem with feet coming off the pegs but have been smacked in the shins with sticks before. I say go ahead and "risk" it and ride the bike a little, at least to work out this bug.

Aight,
I just recently dealt with this problem when I dropped my 42 pilot in.
With the mixture screw set at stock,2 1/4 turns out, I noticed a hesitation when punching it from idle. I turned the mixture or pilot screw
in 1/4 turn and then another 1/4 to get rid of the hesitation. I would try this first and yes the motor needs to be warmed up. I rode this Sat and noticed my header gets a bluish color for the first 5 inches coming out the cylinder. So I turned the pilot screw back out to 2 1/2 turns and it doesn't have the hesitation. You have to fine tune some which isn't hard, and like 3punksdad says, let us know your air mods and jet sizes.
John

[Warrioreater400ex]

well, my airbox has no mods, and it has a 155 main jet in it...... but thats about all i know

Take your airbox lid off, warm the engine and see if it still hesitates.
I would think you need to let some more air in, maybe by installing air vents, the round kind that Dennis Kirk or Rocky Mountain sells.
John

[Warrioreater400ex]

thanx for all the advice..... i been ridin it a lil longer..... and the flat spot disappeared after it got warm :D , which i am glad of.... so i hope that its just acting cold.......