Help want to know good 400ex build

[Mtndew99]

Hi I'm new to the forums and this winter I am going to be tearing down my 2002 400ex and I've had it for about 2 years has never broke down on me and I want to start racing harescrambles (new east coast xc) and I am fairly good on a quad and want to know a good motor build I've been thinking of a 426 kit 11:1 compression with a stage 1 hot cam and re seat the valves and clutch kit and basket.....just want to know what brands and such wld be best and more opinions on a good setup

[CJM]

Just do a hi comp 407 setup. Theres no reason to bore it out unless you need to. It wastes remaining bores you have left once you go as high as 426. Your not gaining much either.

The power comes from the hi comp piston setup. I wouldnt bother with a stage 1 cam, friend of mine has one and seriously lacks power vs my setup and his is the same except for a smaller bore. Hotcam stage 2 is what you need to run, its a good all around cam.

Stock clutch will hold up fine. You want slightly better grabbing power buy the GT thunder setup. I got one and love it-but its nothing more than 250r clutch fibers and plates and a machined plate with some HD springs.

You will want to do the rear shock up for long travel to alleviate the horrible bucking from whoops the short swingarm produces. GT Thunder again is what you want. You will need to remove the skid and buy or make a custom skid to fit the linkage. Got the setup on mine and love it.

Steering stabilizer is a must, I got a CCP (its on ebay) and it reduces bump steer considerably and helps handing if you hit anything like a rock, stump, etc.

Switch to razr 2 front tires 21x7x10 and razr 1 tires 20x11x9 or 22x11x9 (depends on what ya want). Thats the setup ballance always used.

Redo the front shocks with some 450r reworked shocks.

Dont gotta do all of that but it will help greatly.

Also make sure your allowed to whatever you want to the quad for your race series. Some have restrictions.

[WoodTRD]

I'll second the stage II cam from experience, I have a stage 1 and love it's bottom and midrange, my ex has the power curve of a pool table and will loft the wheels pretty easily in low fifth gear, but I know a stage two would let it breathe better up top where it falls on its face when running it all out.

The overall best mod for the buck I have done for my ex was the 450r front shocks, even not reworked mine are miles ahead of the stock pogo sticks...but I weigh around 215 and have everything set most of the way to soft, they may be a bit stiff if you're lighter and don't get them reworked to suit you.

A close second was my 450r carb, it made a huge difference on my bike the way it's setup...but I would wait till after the motor work is done to get the full effect.

If you're building your motor yourself I would run a cometic MLS thin head gasket and no base gasket, that bumps the compression up roughly another .5 over where it would be with stock gaskets and actually helps it run cooler due to the better flame distribution across the piston...my bike runs cooler now than it did with stock compression and +6 timing.

Just some ideas but remember, you can only go as fast as you can handle the bike, suspension and a steering stabilizer will be a must.

[DragonGunner]

Been there done that with the 400EX....stock, 416, 426, 440....I like my 406 11:1, port job....I ran stock cam an then went to a WEB cam which is probably close to a stage 2 Hotcam.....That cam looses a little on bottom, but what I found is I spin too much in slick stuff or in mud, the stock performs better. Getting a great suspension is going to be your ticket to not getting beat to death an finishing strong.

I ran stock clutch, still on the original from my 99', just put HD clutch springs in it in 2000.....too many clutch cables to remember....lol.

[Mtndew99]

I have shocks being built right now money isn't a problem I got elka with laeger long travel a arms on the way and next ill get a rear shock or even my stock one re done with gtthunder linkage