400Ex what do you recommend

[Lilunwl]

Hello all im new to exriders and thus far i like it! I have a 2002 400ex and am going to start modding it and would like some others opinions. It is currently all stock.What i want to do is concentrate on a snappy throttle looks will come shortly after.I dont want to bore it because ive heard from others that its pretty much down hill after you do that. So what i am asking is if it were you and you had a stock 400ex what would you do to have it running the best or close to the best that is possible. I ride mostly trails but have fun racing against friends. What would you do first through last? someone i was talking to said something about a 450r carb. and ive seen it on here as well. Where do i find out what years will work on my bike. Is this really something that i should do? Well anyways thank you in advance to all who help me with what to mod on my bike to get as much as possible out of it.

[BossHogg420]

dont get the carb unless up go up in compression or bore out. for snappy response u could lower the front sprocket a tooth....cost u 10-15 buxs or get a sparks advanced timing key....cost u 20 plus 10 shipping and the 15 dollar gasket. get an uni air filter and outerwears on the filter so u can take the airbox lid off for more airflow...matched with a slip on exhaust and u'd nice some nice power!

1) 450r carb
2) Curtis Sparks timing advance key
3) Air filter
4) Exhaust
5) XR400 head gasket


That right there will make it run pretty damn good but just as reliable as stock. Mine seems to pull pretty good even without the carb and thinner gasket.

If you still want to be reliable and want even more punch, add this to the list:

Wiesco 11.1 or 10.8 piston
Hotcams Stage 2

[Pipeless416]

i agree with the above. a 450r carb WILL be beneficial, even to a stock engine.

[Lilunwl]

So what is a sparks advanced timing key???Is this pretty simple to do? Im confident in pretty much anything external of the motor but not internal.Is this an external componant? So far wow i cant believe the helpful responses in such short time.!!!Thanks and please if theres other ideas please feel free to add.Im very open minded on what i do im just looking for what seems to be either mentioned most or what others have done with sucess.

For under $150 you can get:

advanced timing key and gaskets $45

open the airbox lid FREE

grind down the header welds FREE

remove the choke FREE

New airfilter K&N with an outerwear or UNI. put an outerwear over the airbox aswell to keep it drier and less dirty too. $75

Rejet $20

**prices ar estimates you might find a part cheaper or more expensive. I rounded up to make it a 5 or a 0.

I bought my HMF, K&N, both outerwears, advanced timing key and gaskets, and jets all for $215!!! The only new performance parts that were boughten is the airfilter, both outerwears, and jets. My HMF and timing key were both used. Look for deals. You can find some really cheap used stuff thats in perfect condition. Part outs or rollers are a great way to pick up some mods inexpensive.

[hypersnyper6947]

Originally posted by DMC-4OOEX
1) 450r carb
2) Curtis Sparks timing advance key
3) Air filter
4) Exhaust
5) XR400 head gasket

Wiesco 11.1 or 10.8 piston
Hotcams Stage 2

I say do all this and some port work and you'll be good to go.

Then its on to the suspension ! :D

[400ex07]

If you are comfortable with external mods start with a new air filter, exhaust, and jetting. If you have the right tools do the sparks timing key. There is an awesome right up on this site on how to do it. Don't waste your money on a 450r carb right away. You might be happy with just those mods. also if you ride trails i would go to a smaller sprocket in the front. I bought this kit from mods3 and I love it. http://www.partsforatvs.com/default.asp?p=2224&c=725&cn=M3Q+400EX+POWER