400ex power adders

[5.0bronco]

Hey guys I just got my first 400ex a few month ago and this weekend it started leaking oil between the head and cylinder on the right side of the engine. Im gonna re do the top end on it and I was wondering what a good setup would be. I was thinking a wiseco11:1 piston with a xr400 head gasket and hondabond for the base gasket and a stage 2 hot cam. Would I be able to run pump gas and would this be a reliable setup? I was also gonna put stronger head studs in it cheap insurance. Is there any thing else I should do while I have it tore down to make it more reliable and perform better? Im New to the 400ex and would greatly appreciate any tips and info.

Thanks,
Ross

[5.0bronco]

O and mines a 2003, its STD bore, it has a yoshi slip on, the air box has been opened up and its been jetted accordingly. I was also thinking about putting a fcr carb on it off of a 450

[81dasher81]

yes, you can still run in on pump gas, you'll just need 93 octane.. i like JE or CP pistons, rather than wiseco but thats just my opinion. i would go with the hd studs if i were you. i got mine from extreme tech racing.. thats a pretty common set up for a 400ex. as far as the carb goes, it depends what kind of riding you do, and if you want smoother power or more snap.. an fcr will make it rev quicker, where a trx carb will be smoother. i also lightened my flywheel on mine, it makes it rev quicker, some people dont like to lighten them for trails but i do.

on my 400ex i'm running a uni filter, the trx450 carb, stage 2 cam, and 13:1 88mm piston, (i just used cometic gaskets,) with a yoshimura exhaust (and heres where everyone on this forum tells me i'm wrong) i run this set up on 93 pump gas at everywhere from 500-1500 elevation, and its jetted 55/205.

what you described will still be a very reliable machine. imo, you can't get much more reliable than a stock 400ex, but you arent going to take much away by this set up.

[400man]

so are you not gonna use a base gasket for the cylinder to get more compression? also, use a crf450 timing chain while u got it apart. and yea jus use 93 and jet it a hair rich and it will last a long time

[5.0bronco]

so are you not gonna use a base gasket for the cylinder to get more compression? also, use a crf450 timing chain while u got it apart. and yea jus use 93 and jet it a hair rich and it will last a long time

Yeah its supposed to bump the compression up a bit. And on the timing chain just use a timing chain off any year crf?

[400man]

kinda, i dont know what years will deffinatly work, but just do a quick search on here and u will find all kinds of info on it. its basically like the "heavy duty" aftermarket chains they sell, except less than half their price. just order one off any oem parts website with a good price.

[ben300]

Yeah its supposed to bump the compression up a bit. And on the timing chain just use a timing chain off any year crf?

2002-2007/8...


i believe sometime around 07/08 they changed the cam chain. i got mine from a 2004 i believe off of rmatvmc....it was like $40 vs $90 for the stock ex

[81dasher81]

when i built mine, i also took the rivets out of the head gasket and used the only the top and bottom gasket sheets for a little extra compression

[LxMxL97]

Everyone says do all these little things to bump up compression why don't you just buy a higher comp piston and I recommend JE pistons

[81dasher81]

Everyone says do all these little things to bump up compression why don't you just buy a higher comp piston and I recommend JE pistons

i just used parts i had.. what's wrong with free power? lol. yes, i also recommend JE pistons

[5.0bronco]

Everyone says do all these little things to bump up compression why don't you just buy a higher comp piston and I recommend JE pistons
I dont wanna raise the compression too much I wanna still run pump gas.

[MtnEX]

Everyone says do all these little things to bump up compression why don't you just buy a higher comp piston and I recommend JE pistons

One good reason people don't think about... reduced piston weight, better flame front, etc....

All comes down to how much compression you can gain with the little things, vs how much compression you want and if there is a gap worth the weight from one piston to another.

I don't know what a stock cast piston weighs either. But the closer you can stay to that weight the more chance the engine will have the same smoothness of operation it did and not vibrate itself to an earlier bottom end failure being that most don't tear an engine all the way down and send the entire assembly out to be balanced, etc....

[5.0bronco]

I think im gonna go with a 440 kit with a 10.8:1 je piston, stage 2 hot cam, crf timing chain, gtt head studs, yfz450 carb and gtt full exhaust. Im around 800 ft elevation any idea where I should start at for jetting?

[LxMxL97]

I think im gonna go with a 440 kit with a 10.8:1 je piston, stage 2 hot cam, crf timing chain, gtt head studs, yfz450 carb and gtt full exhaust. Im around 800 ft elevation any idea where I should start at for jetting?

Where do you ride? What's your suspension consist of?

[5.0bronco]

Where do you ride? What's your suspension consist of?

Mostly trails and track. And my suspension is stock but once o get it running again im gonna get some +2 +1 a arms with Elka or works shocks all the way around