performance up grades

[rdstoner]

what are some cheap and/or free upgrades i can do to get a little more power out of an 03 400ex all i have done is a hmf slip on and a k+n filter i already know about the 6 degree timing advance an i am going to buy the key and do that i just didnt know if there were any other mods i can do?

[DuwBra]

Grind down the header welds, remove the choke, an aftermarket rev box will allow it to rev more and also helps it start up quick. You could also get into playing with the gearing, but that only switches your power from acceleration or more top speed. You could always just clean everything really good, I dont really think it does anything but after i clean i feel like i made my quad happy and it wants to run better ha ha.

[drew416ex]

Also just doing general mainenance. A good quality oil will help the performance you do have last longer. And believe it or not, keeping you chain lubed will help out. A non lubed chain can cause you to lose around .5 hp to the rear wheels. Its not much, but every little bit helps.

[rdstoner]

when you remove your choke does it make it start harder because i ride my quad in the winter sometimes and i dont want to spend my riding time trying to start it?

[rideracelivemx7]

42 pilot jet and crack the throttle two times and it will start easier and better. thats the side affect f removing the choke but its only a cheap jet.

Originally posted by DuwBra
an aftermarket rev box will allow it to rev more and also helps it start up quick.


that is not so true...us guys in the colder areas kill batteries because of aftermarket cdis.. most were not made for the 400ex, the cdi box comes from an XR250 kick start bike. It's equipped with a circuit designed to help keep the engine from "kicking back" on the rider.

What it essentially does is not fire the spark plug if the engine doesn't crank
above a certain RPM. This preset RPM level is just barely under the normal
crank speed of a 400EX... So, throw in some thick oil & cold temps, or simply
a low battery, and it's just enough to cause the engine not to start.

i know in one day, when i had one in my 400ex, i killed the original battery in the 400 AND a brand new one i had just put in my wifes 300ex.

plus the stock bike quits making power well before you get into that extra 1000 rpm range so you don't really notice it

[DuwBra]

It works fine down here, and my cdi noticeably improved my revs of my quad from acceleration to top end, it was a good buy for me anyways.