engine prep for mx

[MrTrendy1]

I am wanting to start doing MX with my 400ex and right now its stock except for jetting and slip on. I know I need to get some suspension first but as for the engine, what do you guys suggest that I do? I want to know so I can start my piggy bank up to pay for this crap.

[Toadz400]

Bore kit (416-440), stage 2 cam, high compression piston, porting and polishing, 39mm carb, and a full exhaust will make a huge difference.

[MrTrendy1]

I have a 04 model and I've read everywhere that the carb is a 38mm, you think that it should be changed?

[Toadz400]

Originally posted by MrTrendy1
I have a 04 model and I've read everywhere that the carb is a 38mm, you think that it should be changed?

It's a typo, the carb is still a 35.5 I believe? Or something like that...go with the 39mm, it's an awesome upgrade, especially with all the mods that I listed. My friend has that set-up with a 416 kit, it pulls like a mother!

[MrTrendy1]

I was thinking I'd probably go 416/426 first off. Did your friend have his done by someone or do it himself?

[Toadz400]

My friend did it all himself, even the porting and polishing. He was only 15/16 when he did all of that too. As long as you know what you're doing, and you have a manual (don't NEED it, but it helps a lot for quick reference), you can do a lot of things.

[MrTrendy1]

I'll do most of the mechanics myself but as for the machining, I'll take it to someone. I don't have the equipment to bore my cylinder out or port and polish it. What exactly is porting and polishing?

[Toadz400]

Originally posted by MrTrendy1
I'll do most of the mechanics myself but as for the machining, I'll take it to someone. I don't have the equipment to bore my cylinder out or port and polish it. What exactly is porting and polishing?

You smooth out the intake so the air/fuel mixture can move faster and there is less resistance, aka: allows more HP to be produced faster.

[MrTrendy1]

Thats what I figured it was. I'll have to find me someone to do the machine work here locally. Hopefully all of this won't cost me to much and I can get this stuff done fast.

[smith_400ex_213]

get an air filter and go with the 426...web cam port adn polish korilla rod adn a hi rev cdi sheel haul u ne were

[MrTrendy1]

I've got the air filter and I planned on going with a 426 and probably a hot cam. As for the rest of what you said, I'll decipher that code and get back with you.

[400-416EX]

I just got a 416 and a full race port and polish, with a edelbrock carb bored for the 416, with a stage 2 hot cam, uni air filter and a e2 pipe and the thing hauls like you could not beleive.

[MrTrendy1]

What size carb did you get? Bored to what size?

[mattyk1221]

do u guys think ots better to get the 450r or fully trickout my 04 400ex???

[MrTrendy1]

If you have the money, sell the 400ex and by the 450r and mod it. I don't have the money to do that so I am going to mod what I have. Not fully trick it out just yet but give myself something to work with and learn to ride MX with.

[400-416EX]

I got the quicksilver and sent it to edelbrock and told them what size motor I was getting and they bored it. I am a honda man myself but if I was gonna sell my 400 for a new quad I would get the yfz instead of the 450r. Good luck with whatever you decide to do

[quadkrazy400ex]

im 15, and i just got done a couple of weeks ago putting in a 416 kit with a ross 10.8:1 comp piston, i went with a stage 2 hotcam too. i can tell you one thing, there is a huge difference in power, it pulls alot harder and is alot faster. i recommend doing what i did, im thinking about starting racing so i decided to go ahead and get the engine ready. i got a good manual off ebay, and i did it all myself. As far as porting and polishing your head, in my opinion i would leave it to the pros, send off the head if your going to go that route. heres the link to the manual that i bought, cheap and had all the info i needed, and then some.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1&item=7917273292&category=34240#ebayphotohosting

[400-416EX]

You can't go wrong with a good maual I would not do anything on my bike with out one. They arfe invaluable, no matter how much is cost you. I actually got my bike all set up for mx and I saved tons of money by buying alot of my parts on this site.

[smith_400ex_213]

Originally posted by MrTrendy1
I've got the air filter and I planned on going with a 426 and probably a hot cam. As for the rest of what you said, I'll decipher that code and get back with you.
whoops sorry i didnt realize it was that bad
web cam
port adn polish
korilla rod
hi rev cdi...
o and hes also running a stock carb and beating some yfx and trx 450's cuz he a good rider in the Wisconsin Quad Series B-class
now she'll haul u any were

[MrTrendy1]

I do plan on doing everything you listed, except the korilla rod. Never really thought about doing that. The high rev cdi is a must if I hit the rev limiter constantly. They are not that expensive either so I don't see why I shouldn't get one anyways.

[400-416EX]

Have fun building. You will really enjoy the bike when your done.

[mps5000]

don't forget mx tires
then a widened axle