New 400ex owner, have some questions

[EHG]

I just got a 2002 400ex first one of these I've had. Im thinking about doing a big bore kit, everyone says 440 is unreliable and I should go with 416 or 426, can I get some opinion on that? I also want to put on a 450r stock carb and Hotcam. Anything else I should look at doing? I already have HMF slip on exhaust and UNI air filter.

Mine has 450r front shocks. Can i adjust them myself or would i have to send them off to be revalved? Im about 200lbs and mostly trail ride but also plan to travel to mx tracks and dunes, how should i set it up?

[DragonGunner]

I've had all the bore sizes on my 400EX….everyone will have a different opinion, All I can say is that I now have a 406EX and it'll do what the 416, 428 and 440 would do. I recommend a higher compression piston over big bore any day on the 400EX, take the money saved and do a port job. Also a longer swing arm and revolved rear shock will help a lot, couldn't live without a Lonestar +1.25" swinger anymore…..If I started all over that longer swinger and suspension would of been priority one over the engine. Most send the stock 450r shocks out….but being your weight play around with, you can adjust preload on the springs and compression settings….you may like them like they are. I run 11:1 compression, slightly higher cause a had the head plained a little, the 440 is reliable until you go higher compression then you have to watch things….like a 12.5:1……I needed GT thunder head studs to stop blowing gaskets.

[EHG]

Wouldn't higher compression put more stress on the bottom end? I dont want to make it unreliable, and i want to be able to run it on premium pump gas.

What does the longer swing arm do for you?

[CJM]

11:1 is what you can run on 93 octane and it will REALLY wake the bike up. I did several builds and found I liked the high compression overall the best over a bore job any day. Your not boring it enough to really increase the displacement by much. A hi comp piston, stage 2 hotcam, open airbox will REALLY wake the bike up a lot.

[DragonGunner]

Wouldn't higher compression put more stress on the bottom end? I dont want to make it unreliable, and i want to be able to run it on premium pump gas.

What does the longer swing arm do for you?


The longer swing arm makes the 400EX feel way better, going to soak up bumps, ride better, will keep the front down and planted….way more comfortable ride.