More power

[400exrules]

My 400 is pretty stock, mods are in my sig. But what can i do to give alittle more torque or power. Are their any free mods i can do, like the cam mod on the yfz. I'd be willing to spend around $300 or so, but i dont want to kill the reliability, and i want to be able to run off pump gas. (89, or 93)

[nosliw]

remove the choke and play with the gearing to get it how you like it

[flyin#5]

remove airbox lid, rejet
slip on silencer, rejet
high compression piston, possibly rejet
cam



there is a lot you can do with 300 bucks... but all of the mods listed above together will give you great power gains, alone you will see some good improvement though.

Originally posted by nosliw
remove the choke and play with the gearing to get it how you like it

Explain how to take the choke off..

Is there anything else you have to do jetting wise?

[Punk'd]

I say remove airbox lid and rejet.

[nosliw]

Originally posted by Honda MaNiAc 01
Explain how to take the choke off..

Is there anything else you have to do jetting wise?

http://www.atvriders.com/articles/choke400ex.html

Get a fmf header and rejet.

[400exrules]

what could i do with around $500? Im torn between two things. I drag raced at the local dragstrip for the first time saturday, and i brokeout both runs, but i think i have fallen in love with it, but i like ridin trails too. So im gonna have to either keep my bike balanced or make it a pure trail bike, or get a big swingarm and go drag

[400exstud]

For 300 you may be able to go with a 11:1 std bore piston and a stage 1 or 2 cam. These mods will be enhanced with your pre-existing slip-on.

[Robin Hood]

Grab a full pipe, drop the airbox lid and rejet? Just my 2 cents.

[400exrider707]

Originally posted by 400exstud
For 300 you may be able to go with a 11:1 std bore piston and a stage 1 or 2 cam. These mods will be enhanced with your pre-existing slip-on.

Yeah do this it is definitely worth the money!

[JRP]

Originally posted by 400exrider707
Yeah do this it is definitely worth the money!

agreed

[bwamos]

Agree.

11:1 std bore piston, Cam, Valve Springs, Clutch Springs.

If you install yourself (which is easy, you just have to have someone re-hone the sleeve) you should be able to do it at well under the $500 mark. In fact you may be able to grab a used WB header pipe off of e-bay as well to compensate for the additional air flow (cam).

[yamaharaptor350]

Originally posted by Robin Hood
Grab a full pipe, drop the airbox lid and rejet? Just my 2 cents.
yea that sounds good^^ just get a pro design screw on filter adaptor so u get a constant seal and not have to wory about the filer comin loose or moving on u and lettin dirt and water in. An outerwear comes with these kits also

[400exrules]

would the wb's powerbomb header work with my hmf can? And where can i get the 11:1 piston/cam and all that. Would i be able to install it myself? Im kinda scared of tearin into stuff

[nosliw]

fmf powerbomb header will work

[bonified5]

i cut a hole in my airbox lid and put one of those $5 lawn moswer intake filters in there. It beats buyin a powerlid for $80

[400exrider707]

Originally posted by bwamos
Agree.

11:1 std bore piston, Cam, Valve Springs, Clutch Springs.

If you install yourself (which is easy, you just have to have someone re-hone the sleeve) you should be able to do it at well under the $500 mark. In fact you may be able to grab a used WB header pipe off of e-bay as well to compensate for the additional air flow (cam).

I disagree with valve springs unless your talking new stock ones. Heavy duty springs will just put added stress on the cam lobes and rockers and cause premature wear.

[bwamos]

Originally posted by 400exrider707
I disagree with valve springs unless your talking new stock ones. Heavy duty springs will just put added stress on the cam lobes and rockers and cause premature wear.

Depends on the cam really. If you have an agressive cam the stock springs are soft enough that the valve can "bounce" when it closes. Valve bounce/backlash is not a good thing.

I'm not a 400ex expert, so I don't know the strength of the stock springs on it, but the stockers on the 300ex certianly have to be upgraded when you add in an agressive cam.

I'll leave the valve spring issue up to the 400ex experts.

[underpowered]

i say get a good 11:1 piston and a stage one cam. or you can go with a416 piston and stage two cam for only the price of the bore more than a standard bore piston. Topend are relatively easy to do, if yo have any mechanical knowledge and are willing to learn you should be able to do everything but bore the cylinder yourself. it should still be reliable. My 426 could not be much more reliable other than headgaskets.