dusty and muddy conditions with airbox off

[nosliw]

just got back from an awesome weekend in shelton, and while i was cleaning the bike, i notice a lot of dust in the airbox. also the k&n prefilter must have been doing it's job becuase that thing looked filthy too. here's my question- how much power will i loose by puting my stock airbox back on? highly noticeable? will i be running wayyyy to rich?

also i know how the clean and oil the k&n filter but what do you guys do with the prefilter?

quick info if you need it

04 400ex
hmf slip on
152 keihen hex-head main
42 pilot
2 1/2 turns out on fuel screw

thats all i have for performance mods

[Toadz400]

You will lose a noticeable amount of throttle response and a little bit of power by putting the lid back on, and yes you will be running way too rich so make sure to rejet.

Clean the prefilter just like you clean the regular filter, and you probably want to put oil on that also.

[nosliw]

well forget that then.

thanks anyways :D

[LTZ400rider]

to clean the outer wears just use dish soap and water, if ur concerned about the dust just use a foam filter and just clean it alot

[cals400ex]

Originally posted by nosliw
just got back from an awesome weekend in shelton, and while i was cleaning the bike, i notice a lot of dust in the airbox. also the k&n prefilter must have been doing it's job becuase that thing looked filthy too. here's my question- how much power will i loose by puting my stock airbox back on? highly noticeable? will i be running wayyyy to rich?

also i know how the clean and oil the k&n filter but what do you guys do with the prefilter?

quick info if you need it

04 400ex
hmf slip on
152 keihen hex-head main
42 pilot
2 1/2 turns out on fuel screw

thats all i have for performance mods



when jetted at the same air/fuel ratio, i don't think the power difference will be noticable. it may "feel" different with the lid on because it is quieter and the air isn't echoing off your butt from the open air box. i don't know the elevation you live at, but here in the warm months i would run a keihin 155 with a slip on and air box lid off. with the air box lid on, i would run a keihin 150-152. the leaner you go (smaller the jet), the more power you will have to a certain extent. however, it is harder on your motor and it will run hotter than normal.

i would drag race someone with the air box lid on and then off. you will notice the difference is little and maybe nothing at all if jetted correctly. also, the filter will stay much much cleaner.

to clean the prefilter, just wash it with soap and water.

[Toadz400]

Originally posted by cals400ex
when jetted at the same air/fuel ratio, i don't think the power difference will be noticable. it may "feel" different with the lid on because it is quieter and the air isn't echoing off your butt from the open air box. i don't know the elevation you live at, but here in the warm months i would run a keihin 155 with a slip on and air box lid off. with the air box lid on, i would run a keihin 150-152. the leaner you go (smaller the jet), the more power you will have to a certain extent. however, it is harder on your motor and it will run hotter than normal.

i would drag race someone with the air box lid on and then off. you will notice the difference is little and maybe nothing at all if jetted correctly. also, the filter will stay much much cleaner.

to clean the prefilter, just wash it with soap and water.

I'd have to diasgree with you, taking the lid on and off (while rejetting) I've noticed quite a big difference in throttle response and a little "power", if that's what you'd call it.

[Dust_1503]

The K&N with Pre filter is plenty good in muddy and dusty conditions i've ran no lid for Harescramble and moto-x and raced in both conditions for both types of racing and as long as you clean your filter often there is no problem. Or better yet carry extra if your doing moto-x and just pop another on inbetween motos.

[cals400ex]

Originally posted by Toadz400
I'd have to diasgree with you, taking the lid on and off (while rejetting) I've noticed quite a big difference in throttle response and a little "power", if that's what you'd call it.


yeah, i am not saying your wrong, i just haven't had the best of luck for "more" power. removing the air box lid changes my jetting between 1-2 mainjet sizes. what i do is jet my bike, according to plug chops, with the lid on and then i drag race my buddy. we race from 1st thru the top of 5th just to see the differences everywhere. then i remove the lid and do a plug chop until i get the main jet where the plug looks near identical to before. once again we drag race. i will do this in the same day and within an hour. as the temp, humidity, etc changes, so does the jetting and performance of the bikes. i can honestly tell you, even with my 426, my bike isn't quicker in a drag race from 1st to 5th with the air box lid off. one thing i do notice, is coming out of a corner on a track, the bike seems to pull a little better. but, this isn't my riding style since i am not in these conditions much. we mainly drag race. everyone has their own technique. i just didn't find this to help my power output for my riding style. you better believe i have tested this out several times. i just never got the results i have been looking for. i mainly end up with a dirty air filter with no noticable power gains when dragging.