ive read that it isnt necessary to rejet if your only installing a k&n air filter, but i bought a jet kit just in case. i was just asking those who already had done it if it was necessary, i ride at less than 1500ft. im planning on putting an hmf pipe on it later as well.

 

<div class="FTQUOTE"><begin quote>Originally posted by: AC4LIFE

ive read that it isnt necessary to rejet if your only installing a k&n air filter, but i bought a jet kit just in case. i was just asking those who already had done it if it was necessary, i ride at less than 1500ft. im planning on putting an hmf pipe on it later as well.</end quote></div>

The truth is in the sparkplug color. My 400 came from the factory jetted a little too rich as most all do. So you should be fine. K&N won't be at its full use because the intake for your air box is still not big enough. 95% sure your engine will still want more air whether you have a K&N or factory. Read the link 'Air jetting'.
Well let me back up a tad - depends what main jet you already have. My 2003 had a 150 and I think the 2004 had only 145 and I almost think the 2006's have a 140.... What year is your 400?
You could have saved some bucks by just getting the K&N treatment kit and using your stock foam filter, or gone to a lighter oil. I treat my air filter with Marvel Mystery Oil. So far it has worked really good, if it doesn't then I will do something else. When it starts to look dirty I clean it and treat it again.

 

It is always a great idea to check your jetting....even if you're not doin' any mods. As was posted earlier, they're normally jetted rich, considering they go all over the country. The DVX I modded for ATV Sport was surprisingly close even after the Eddie Sander's Racing mods.

I keep a 3 gallon table top parts washer with a diluted Simple Green type of degreaser. This parts washer is used exclusively for my K&N's. Air dry, then I only use the K&N oil. The reason I switched from the K&N brand of degreaser.....just take a sniff (a light one, no chemical snorting please. LOL)of the K&N cleaner, then compare that scent to a bottle of Formula 409 household cleaner. They smell the same. [img]i/expressions/face-icon-small-smile.gif[/img]

 

forgot to mention, its an 03 400 4x4 automatic. the stock filter is on its way out, the airbox was flooded before so i figured if id get a new filter, might as well get that. thanks for the input.

 

<div class="FTQUOTE"><begin quote>Originally posted by: AC4LIFE

forgot to mention, its an 03 400 4x4 automatic. the stock filter is on its way out, the airbox was flooded before so i figured if id get a new filter, might as well get that. thanks for the input.</end quote></div>

Same as mine so you most likely have the 150 main jet in there which is plenty rich enough. The 2004 comes with 142 but I also believe a different cam. I feel the 2003 still has more guts. I'd like to get the specs on both cams to see the lift and duration of each.