Free easy 400ex Mods??

[TYayo420]

ok not to sound cheap, cuz im not and will drop money into the 400ex to gain some power and speed, but on thumpertalk.com i read something abt xr400 motor and bikes having free mods, well im wondering what does the 400ex have? i know it wont gain a huge amount, but just curious is to what i can and should do before i spend some hard earned $$$ on it, which i will be happy to spend some $$$ to get a nice bike.

Basically what i mean is, i hear there is a air box mod, and a couple others, i need to know what they are, and how to do them...

Thanks very much, sorry for asking tons of questions, but this 400ex is my first 400ex and i never really modded my previous wheelers before besides pipe.

[vett_09]

A lot of people run with no air box lid on their 400's. I don't run an air box lid, but I do have an outterwears cover.

The Spark's timing key is $20 and I've heard it's a good performance gain for the money. But I think you can only use it with stock engines, I could be wrong.

[feelthisroost11]

If you remove choke on stock carb you'll get a little more flow.Airbox lid,snorkel,maybe removing the baffel also. i think those are the only things freeing up little power on a stock 400ex ?

[lilhouskey]

Take the silencer out of the exhaust? i know people argue it has little to no effect but its free and it makes your quad sound better and it has to do at least a little bit

[400exrider707]

The choke removal on the carb is in the tech articles on this site.

[dariusld]

Grinding down the header welds. Search for it.

[TYayo420]

Originally posted by dariusld
Grinding down the header welds. Search for it.

i read about that on here actually 3 weeks ago before i had the ex i just got, and before i was a member, this site is ***in awesome as hell i love it.

Someone said remove the silencer and someone else said remove the baffle, well i dont have a stock exhaust, i have a fmf slip on, soo does this still apply t me then? I'll try the airbox lid thing cuz i have outwears covers somewhere, idk how much ill gain off that, but i prolly wont notice but ill try...

What should my next mods be? hot cams stage 1 or 2, or 440 big bore kit? i ride trails alot and do flat track racing, any suggestions? ill do both those mods but 1 at a time then in a month or so do the other, thanks guys!

[Taylor400ex]

You deft. dont need to take at the baffles or the silincer in your exhaust. My two cents from what I've heard is you dont need to remove anything from any exhaust, because you also need "back pressure" for your engine. Just because exhaust escapes your pipe "better and faster" doesnt mean its actually better for your performance.

[lilhouskey]

Originally posted by Taylor400ex
You deft. dont need to take at the baffles or the silincer in your exhaust. My two cents from what I've heard is you dont need to remove anything from any exhaust, because you also need "back pressure" for your engine. Just because exhaust escapes your pipe "better and faster" doesnt mean its actually better for your performance.

True but not to the extent that the stock muffler has, back pressure can help but there is no way that opening up your exhaust a little from stock is bad for your quad unless it really leans out your jetting. and anyway in his case he already has an aftermarket pipe, there isnt much back pressure from an aftermarket pipe compared to a stocker and the performance gains are pretty decent.

[drag93ex]

like said above, removing choke and snorkel. take the choke out and get more throttle response. take off the snorkel and cap the hole with a rattle can (spray paint can) cap, drill holes in cap.

[j450rking]

i wouldn't think taking the snorkel off would do anything

[TYayo420]

Hmm take the choke out? im a little leary about tearing a carb apart, cuz i am no mechainc, all i can do is simple fixes, illlook for a good thread on here for a how to. How noticable are the gains if i remove the choke? low, mid or top?

Now the snorkal lol sorry this is going to sound dumb of me, but what and where is the snorkal? i have a idea its connected to the airbox towards the gas tank maybe? again the gains, are they low, mid or top? and how noticeable?

[miller821]

Originally posted by j450rking
i wouldn't think taking the snorkel off would do anything

Better air flow... The snorkel has to run all around different stuff, and isn't really open to a lot of air...



Originally posted by TYayo420
Now the snorkal lol sorry this is going to sound dumb of me, but what and where is the snorkal? i have a idea its connected to the airbox towards the gas tank maybe? again the gains, are they low, mid or top? and how noticeable?

Snorkle is on the right side by the pipe, the clear tube that sticks about 3 inches into your airbox and runs under your gas tank.

[flauge]

Hey, taking out the choke is a simple fix;) . It took me only like 30 minutes to do. Id say take the choke out, take the lid and snorkel off and rejet it. You'll notice a good difference:cool:

[TYayo420]

i live in NY, where it gets cold, how will i start this with no choke? start it without it and keep revvin it till it idles? cuz my beast doesnt start well in cold with ther choke

[<DRS>GPF]

Originally posted by TYayo420
i live in NY, where it gets cold, how will i start this with no choke? start it without it and keep revvin it till it idles? cuz my beast doesnt start well in cold with ther choke


i think theyre forgetting to mention youll need to replace the pilot with a #42.. or you likely wont get it started..


surely you've adjusted the "slack" out of the throttle.. if not, thats free..


i wouldnt recommend opening the airbox or exhaust without adjusting the main jet.. too lean and the motor will run hot..

not many "free" things.. but there's a few inexpensive "tweaks"..

[dariusld]

Originally posted by <DRS>GPF

not many "free" things.. but there's a few inexpensive "tweaks"..

Sounds like alot of free things to me. If you want more details on all these mods, there is a ton of info here, just search. :)

[TYayo420]

alright thanks guys, i think soon im going to go to a 440 big bore, hmf pipe and re-jet, but i just wanna do the tweaks or free mods first and then do the other things, im gettin everything i want done at once so itll be like a new machine soon.

[blasterman]

Hey would milling the head down at all help because we have a cnc macine at my school and I can use it for whatever I want basicly.?

[Wildbrain]

Cut off your fenders. It will make you more aerodymanically correct.
It will also help with wheelies.

[TYayo420]

yeah me front fenders are race-cut to begin with, im thinking about doing somehting with the backs if i can find a page of different back cuts.

[flauge]

Originally posted by blasterman
Hey would milling the head down at all help because we have a cnc macine at my school and I can use it for whatever I want basicly.? Yea, it would give a lil more compression and a better quench area, or squish. im not 100% percent sure on what that is but i think it will help your engine run a lil cooler and be less prone to detonation..

[dariusld]

Originally posted by flauge
Yea, it would give a lil more compression and a better quench area, or squish. im not 100% percent sure on what that is but i think it will help your engine run a lil cooler and be less prone to detonation..

less prone huh:huh

[400exrider707]

Originally posted by flauge
Yea, it would give a lil more compression and a better quench area, or squish. im not 100% percent sure on what that is but i think it will help your engine run a lil cooler and be less prone to detonation..

It will run hotter and be more prone to detonation... the good side is more compression and more power. Another thought is that milling your head down is going to throw timing off slightly, which can be counteracted with an adjustable timing sprocket. I would take the lid off and not worry about the snorkel, and put a 42 pilot jet in. I had one in my EX here in NY too and never used the choke once again, even though I did leave it on the carb. The 42 pilot is a must for starting the EX, all your cold blooded worries are gone!

[flauge]

Im still kinda skeptical about the running cooler part and being less prone to deto. too even after reading up on it. Here's a little info (http://www.chevyhiperformance.com/techarticles/94138_piston_head_clearance_guide/) i come up with..

[DF400ex]

Originally posted by TYayo420
i live in NY, where it gets cold, how will i start this with no choke? start it without it and keep revvin it till it idles? cuz my beast doesnt start well in cold with ther choke

I live like 5 miles from you in South Byron. I wouldn't advise taking the lid off or snorkel in our area. It'll work fine in the summer but as soon as it rains you'll get a ton of water in your air box. I have six one inch vents on my lid and it allows alot more airflow than just a straight air box. From Sept-April it's too wet on the trails for a wide open lid. Or you could just take the lid off in the summer and put it on when it's wet later. Just make sure you rejet it.

Higher compression = more prone to detonation. That is why when you put a 11.0 or higher comp piston in you must use race fuel, or atleast 93 octane. The higher the octane the less prone it is to detonation.

To start it in the winter just turn your idle screw up a little till it gets warm. I hardly ever use my choke, if ever.

Where around here do you ride btw?

[Flyin400]

K&N filter works good for cheap easy power

[400ex=awesome]

my raptor 700 had 55 hp on the dyno and then we put the quit cores/ silencers in it and it gain 3 1/2 hp acyually!

dont take out the silencer bc if you loose back pressure you may loose power...

[JOHNDOE83]

Originally posted by 400ex=awesome
my raptor 700 had 55 hp on the dyno and then we put the quit cores/ silencers in it and it gain 3 1/2 hp acyually!

dont take out the silencer bc if you loose back pressure you may loose power...

Four strokes dont work with back pressure in the exhaust, thats 2 strokes.

four stroke produce more power with less back pressure.

[JOHNDOE83]

Also, completly removing the airbox will gain you power.

you have to up jet to accomodate.

anyone who disagrees has no idea what they are talking about...lol.

its a very easy mod, you leave the snorkel to support the intake tube and just remove the plastic box.

if you dont do alot of wet riding and keep the filter oiled and clean, its fine.

[IMSROLL450R]

Holy crap talk about resurrecting a dead thread......

the best free mod you can do is call to come pick up your quad. lol just jking. man just spend a lil money and get a pipe and cam. that will help you a lot. if its stock go with the stage 1 if your going to mod it later go with the stage 2 cam.