Hi there I just got a new 07' Honda 400ex. Best quad I have ever owned. I was wondering what simple mods I can do to it to make it a little faster and run better. I want to get the most out of my 400ex. I am looking to keep it mostly stock. I dont want to get an aftermarket exhaust because of the price and they are too loud for where I live. I have been looking at those aftermarket end caps for your stock exhaust, but I dont if I would get a lot power from that. Are there any ways to make the stock exhaust sound better? Any thought would help, Thanks

 

hey man, got same quad, in the same process you are. i took the spark arrestor off of mine and it sounded like a harley so i cut the spark arrestor off of the end cap and that gave me a noticeable increase in power and made the bike sound like it had an aftermarket exhaust but it is still not as loud as the aftermarkets. im getn an air filter(UNI or K&N)and then im doin an airbox mod. doin all this needs jetting though so im gonna run a 150 main(2 sizes above stock) and a 42 pilot.

 

hey man, got same quad, in the same process you are. i took the spark arrestor off of mine and it sounded like a harley so i cut the spark arrestor off of the end cap and that gave me a noticeable increase in power and made the bike sound like it had an aftermarket exhaust but it is still not as loud as the aftermarkets. im getn an air filter(UNI or K&N)and then im doin an airbox mod. doin all this needs jetting though so im gonna run a 150 main(2 sizes above stock) and a 42 pilot.

 

you want to keep it mostly stock but get the most out of it??? first off those end caps sound like crap.a slip on air filter and air box mod is all you need. but dont use a K&N air filter they pass more dirt than a foam filter. the fmf Q series isnt loud but cost a bit.any modifications you do to the air filter or exhaust will require jetting.a 42 pilot works wonders on cold starting you wont even need to choke it.

 

Not much you can do to the stocker except maybe a UNI air filter, maybe bent the airbox lid, and uncork the stock muffler. You will need to rejet, because it is jetted lean at the factory (to meet emissions standards), and these mods will make it even worse.

But.....I think you should save your money and don't mess with it until you can afford a set of mods that compliment each other! I would get an FMF PowerBomb header and Q4 muffler. EHS Racing airbox lid with Outerwears (if you don't run in extreme wet frequently), and a ProDesign (ProFlow) adapter with foam filter (avoid K&N!). And of course, a rejet....

 

I would like to ask all of you who seem to dispise k&n air filters why you hate them so? I run a k&n on my '02 400ex and i have no problems whatsoever with it. And by the way those uni filters are junk

 

lol thuff. IMO you should rejet to 42 idle and remove your choke from your carb. This is almost free and will make a difference you will honestly feel. Here is a link EXriders.com, your Honda 400EX, 300EX, 250r, and 250EX resource... after that you should think about saving for an exhaust...if you look at Rocky Mountain ATV you will find Lexx to be really reasonable for price and I can tell you as I have one with the spark arrestor in it isnt loud.

 

oh and I have run K&N with precharger for a couple of years now through the dustiest northwest trails without an airbox on and my quad has yet to have an issue.

 

what i have done to my 400ex is stage II cam, .20 0ver piston, fmf powercore 4 full exhaust,jet kit, and K&N air filter. what else would be a good mod? thinking about getting a cdi box. would that hurt the motor in any way?

 

If you have the stage 2 cam you might see some mild gains from a cdi. For the most part they dont do much. If you do decide to get one order a stock unit for a xr 250r dirtbike. Its the same one as the aftermarket units for the ex.
Look at the very bottom of this page.
http://www.powroll.com/P_HONDA_TRX400EX.htm