What mods should I do to a 400ex

I'm looking to get some more power and style out of my 2003 400ex it got



Handle bars that's it I'm also looking at a 440 kit any suggestions

Up the compression a bit, mild clean up port on the head and a cam

Air shrouds to cool the engine, trx450 carb, trx450 front shocks, the 440 is a great motor. IMO the shrouds are most important.

What stage of cam should I do 1,2,3 I do mostly trail riding and some dunes

Depends where you want the power and how you want it delivered. Most cams have a description of what they do with them.

I got a arm racing stage 3 CID and now my 400 cuts out at about 3/4 throttle. Any help?

I'm guessing you are talking about the AMR CDI, what mods do you have done to your quad, even slight ones?

I have the hmf full pipe KnN and jet kit plus the AMR CID


3 holes in air box lid

Clean carb, pay extra attention to the main jet. You may need to bump up your main 1 or 2 sizes.

Anyone here looking for some real nice aftermarket goodies for their 400? I'm a retired motocross rider- had a 465ex- now took the stroker out and made it a 425, gonna make it a hard core trail quad. But I have a bunch of high quality goodies. Not all the information is there 100% as I have to clean everything up and do a little digging on some of it. Will consider selling the stuff as a lot at the right price or individually. I will post more, once I get more pictures and information together.



Brand new powdercoated red Gibson swingarm (gibson is East Coast ATV brand) +1- new, never been used- new price was $430- asking $300


Roll design control arms (bottom arms have been powdercoated red and never used since powdercoat- have new control arm bushings- uppers have minor rust on chrome), missing tie rods and ball joint bolts - new price is $1100+- asking $500 as is- or if you want the tie rods and ball joints I'd include them for $600


Burgard Cycles (Hellbound Racing) +1 Steering Stem (chrome)- used- with standard clamp- new price is $200+- asking $100


Burgard Cycles chrome +1 swingarm- used- asking $150


Pep Steering Stabilizer (grey)- brand new-never used- msrp new is $140-$170- asking $70


Burgard Cycles control arms set (not sure if they're +2 or +3. I have to measure them)- $450 new- asking $100 if I can't find the tie rods, $150 if I do find them


Rear brake assembly (master cylinder, reservoir, rear caliper-has NACs Racing caliper E-block)- $30


Aftermarket rear axle- not sure if it's Durablue or RPM- 99% sure it's a Durablue- has sprocket and sprocket carrier and wheel hubs- used- asking $150


Durablue adjustable rear link/strut- used- new $115- asking $50


For everything together- that equals $1550- however- I'm willing to do a package deal of $1200 if you buy everything- which is a hell of a deal


If you're interested call or text 610 849 6507 (please no spam) My name's Chad- in the meantime I will be cleaning the dust off of everything and taking pictures, here are a couple of pictures I took of the Gibson swing arm









If you're wanting more power, get a Banshee (:

If you're wanting more power, get a Banshee (:


Banshees are over-rated. A 250r will walk the dog on a Banshee any day. Unless you're riding in straight lines. And a tricked out 450 (Yamaha or Honda) make 90% of all quads seem slow, even my 465 didn't have nearly the torque/weight ratio like these new 60hp 450's (basing that number on my friend's 15:1 compression ratio pro-am Honda)

Cut a hole in the air box lid 1/2" from the back

The 440 kit is due for a rebuild every 50 hours but the 460 kit is do for a rebuild every 75-100 hours I believe correct me if I'm wrong mine did the same thing but gas was leaking out of the carb a cleaning solved it all I wouldn't suggest the big bore kits because it loses it's reliability

I've run probably every version of the big bore kit for the 400's- the 416, 425, 440, 465 and 505 and even an experimental 535. And since no one's racing a 400ex since the 450's are so much more powerful, I'd go with the 416 or 425 personally. The 416 and 425 are a very strong running motor that don't require as much upkeep if you do it right. Never run your tolerances too tight, because as the engine expands with heat, it will cause issues. Running looser tolerances might not make quite as much power, but it's more reliable (obviously don't go too loose). If you do the 416/425, do a cam, a flat slide carb and port your head and you'll be amazed at how strong that thing runs. You should be able to go a couple years (depending on how much and how hard you ride) without replacing rings. But if you want ultra reliability, just leave the motor stock. They're pretty bulletproof stock and if you upgrade the air filter and pipes and carb, you can at least get a little more out of it.

Nerf bars!!!


Edited by Ny00400ex

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