400EX free mods?

[Dangerous400EX]

I am the proud owner of a new '07 400ex and I am pretty new to ATV's, so I am going to keep the machine mostly stock for awhile. I know with everything there are some cheap and free mods that can be done to increase performance.

I have read about removing the air box cover, does this really make any kind of difference or does it just make the air filter dirty a lot faster?

Also does switching the front tires inside out add enough stability to be worth it? Does it cause any problems with the front brakes?

I am probably going to drop the front sprocket by one tooth, I am more interested in acceleration and holeshot than top end. Does this make much difference on a stock machine?

Should I be looking for some spacers for the rear axle, or are they hard on the longevity of the axle? I want to keep this machine pretty maintenance free, I have enough things to wrench on.

Thanks, any other tips would be appreciated.

[justin1022]

Originally posted by Dangerous400EX
I am the proud owner of a new '07 400ex and I am pretty new to ATV's, so I am going to keep the machine mostly stock for awhile. I know with everything there are some cheap and free mods that can be done to increase performance.

I have read about removing the air box cover, does this really make any kind of difference or does it just make the air filter dirty a lot faster?

Also does switching the front tires inside out add enough stability to be worth it? Does it cause any problems with the front brakes?

I am probably going to drop the front sprocket by one tooth, I am more interested in acceleration and holeshot than top end. Does this make much difference on a stock machine?

Should I be looking for some spacers for the rear axle, or are they hard on the longevity of the axle? I want to keep this machine pretty maintenance free, I have enough things to wrench on.

Thanks, any other tips would be appreciated.


the air box lid dont relaly do anything unless you got other mods done to your quad and the insdie out rims.. ha my freind did that to his ltz and he crashed 1 time and it bent his spindles so i would do it and the rerst i never tryed.

[justin1022]

Originally posted by Dangerous400EX
I am the proud owner of a new '07 400ex and I am pretty new to ATV's, so I am going to keep the machine mostly stock for awhile. I know with everything there are some cheap and free mods that can be done to increase performance.

I have read about removing the air box cover, does this really make any kind of difference or does it just make the air filter dirty a lot faster?

Also does switching the front tires inside out add enough stability to be worth it? Does it cause any problems with the front brakes?

I am probably going to drop the front sprocket by one tooth, I am more interested in acceleration and holeshot than top end. Does this make much difference on a stock machine?

Should I be looking for some spacers for the rear axle, or are they hard on the longevity of the axle? I want to keep this machine pretty maintenance free, I have enough things to wrench on.

Thanks, any other tips would be appreciated.


o yea and for free mods you can remove your choke it isnt really needed i did it and it increased a bit of throttle responce

heres some free mods, you can thank gordon for some of them off of a XR400.

-remove the choke, install a 42 pilot
-grind down the header welds
-remove the airboxlid and jet if your all stock try like a 150 main
-drill holes in the stock baffle or cut out the spark arrestor, cut out the center metal piece and weld the spark arrestor screen back in I dont know if you will need to rejet for that
-I just thought of this cutting the cage for the stock airfilter or drill in holes so it will flow more and it wont collapse like if you removed the metal cage.


there not completely free because you have to buy jets but its pretty cheap. For under $60 you can really wake up your 400ex from stock if you add the 6 degree ignition timing advance, do those mods and jet for it.

[RaginRedneck]

If you drop a tooth on the front sprocket you will notice a major difference! 1 tooth in the front is equivalent to about 3 teeth in the rear, and stock or not, it will get you some ripping good fun.

[rideracelivemx7]

to me spacers for the acel are a waste of time and money. yeah they make it look cool but not worth it.y buddy had +1.5" on his and i said they will snap or bend something real quick. he said yeah i know but they look good. in 2 weeks of good riding he created a nice wobble in each hub. in 3 weeks he said, hey do you know where i can get a set of new hubs? i just broke off the right hub studs lol. the spacers create a huge about of stress on this hubs them selves.

as for removing the airbox lid. if you jet the bike just a little out then you can remove the lid. if not then running stock with the lid off you actually loose hp up top.

[400ex28]

Originally posted by FoxHondaRider
-I just thought of this cutting the cage for the stock airfilter or drill in holes so it will flow more and it wont collapse like if you removed the metal cage.


It wont collapse

Originally posted by 400ex28
It wont collapse

good to know but i wouldnt remove it because it keeps a tight seal and then you have a hole in the back of the filter so I suggested cutting parts out or drilling

[Dangerous400EX]

Originally posted by RaginRedneck
If you drop a tooth on the front sprocket you will notice a major difference! 1 tooth in the front is equivalent to about 3 teeth in the rear, and stock or not, it will get you some ripping good fun.

Thanks for the reply, the stock sprocket on an 07 is a 14 tooth sprocket, correct?


Thanks for the other replys on the spacers and front wheel switch, looks like I will leave them alone. You guys that have jetted up, do you have any problems with harder starting or running too rich and fouling plugs? I wonder why Honda leaves them lean from the factory?

Originally posted by Dangerous400EX
Thanks for the reply, the stock sprocket on an 07 is a 14 tooth sprocket, correct?


Thanks for the other replys on the spacers and front wheel switch, looks like I will leave them alone. You guys that have jetted up, do you have any problems with harder starting or running too rich and fouling plugs? I wonder why Honda leaves them lean from the factory?

they do that to pass emission tests. i have seen cars purposely run lean so when they go for inspection that 1 run on the dyno or w/e its lean and isnt producing as much carbon and anything like that.

[400ex28]

Originally posted by FoxHondaRider
good to know but i wouldnt remove it because it keeps a tight seal and then you have a hole in the back of the filter so I suggested cutting parts out or drilling

I put rtv sealer over the hole.

about the spacers i know a guy that put some on his ltz 400 and he ended up bending his axle. idk if it was from the spacers or what but just a heads up

by the way my 400 is bone stock to so don't feel bad

[RaginRedneck]

[QUOTE]Originally posted by Dangerous400EX
[B]Thanks for the reply, the stock sprocket on an 07 is a 14 tooth sprocket, correct?

Stock on an '07 is a 14 tooth. I bought a 13 tooth for like $15 from the local dealer, quick easy install, and the gain is great. You lose a lot of top end, but I can't get out of 1st gear fast enough, second and third are monsters as well.


Good luck

[NacsMXer]

On bone stock 400EX's, adjust the slack out of the throttle cable, it doesn't open all the way from the factory!

Originally posted by NacsMXer
On bone stock 400EX's, adjust the slack out of the throttle cable, it doesn't open all the way from the factory!

yeah i've been running mine like that since I got it never realized it until a week ago that at full throttle the slide is only up 6-7/8th

[Dangerous400EX]

thanks for the suggestions, a new sprocket is on the way. Eventually I will probably jet up as suggested as well.

You guys without a choke, how does the bike start in the cold? I bought a Honda because I wanted something that will start. I will look like a real dumbass if I have to crank and crank the thing because I removed the choke on purpose lol.

[NacsMXer]

Originally posted by Dangerous400EX
thanks for the suggestions, a new sprocket is on the way. Eventually I will probably jet up as suggested as well.

You guys without a choke, how does the bike start in the cold? I bought a Honda because I wanted something that will start. I will look like a real dumbass if I have to crank and crank the thing because I removed the choke on purpose lol.

When you remove the choke you first need to plug up the hole real well with something. Then replace the stock pilot with a 42 pilot and it should start up a lot easier than stock without fumbling around with the choke. When it gets colder out, all you have to do is pump the throttle a couple times before you start it (your carb is equipped with an accelerator pump). That will squirt enough fuel into the engine to let it start smoothly. The 42 pilot makes a big difference.