needs a rebuild

[vroom]

alright guys here's the deal. My 400ex is SLOW, the guy i bought it from bought it off his friend who bought it brand new , in other words im the 3rd user, they were pro snowboarders, college kids, and i think they just didnt know how to break it in and ran the hell out of it from the start. its mods are in my sig... anyways its reallllll slow, like bottom end its nasty but mid range and top end feels like it just revs out, like its not trying... i think im just gunna bore it out a bit and break it in the CORRECT way. How should i go about doing this? I think i want a 416 kit, nothing more then that i don't think, and can I install the 416 kit myself with a sleeve or whatever? What are my options for going about this, any input would be greatly appreciated. thanks

- tom

[Silverfox@C&DRacing]

You can do the 416 yourself if you are mechanically inclined and have a manual and tools.
The 416 does not take a sleeve you take your cylinder to a machine shop and have them bore the cylinder when you get the piston.

You can do just a piston kit but you will benifit more with a piston and and cam.

there are many threads on the 416 topic with good info if you do a search.

[cals400ex]

if it feels like it has no power then:

make sure the throttle cable is adjusted. if there is too much slack, the carb won't fully open when you actually have it pinned.
check your jetting. with your mods known, someone on here can give a good guess on what your jetting needs to be at. make sure you tell us if you are using a jet kit or keihin jets. there numbering style is different and it confuses some people. if its not burning oil or making wierd noises, it probally doesn't need to be rebuilt. however, a 416 with a cam will wake it up. yep, no need for a new sleeve unless your going bigger than a 426. just have a shop bore it out. if it is ticking pretty bad, i would adjust the valves. make sure the air filter is clean. with this bike, change the oil on a normal basis. also, with those 18 inch tires, you might want to gear your bike a little higher if you are interested in top speed. if you prefer tight trails or a track, that low gearing is probally just fine. with reading and understanding the owners manual, i think you can do it. i did it a little while back without any problems.

when you say your 400ex is slow, what are you comparing it too??