jtm994

i have a 400ex 02 atv and i cant seem to get it to run right ive tried everything and the last thing i can come down to is to rejet the carb. can anyone kinda explain on how to do it or a write up would be nice to see if anyone knows of on. thanks

1999runner

http://forums.atvconnection.com/cate...fm/catid/8.cfm

jtm994

yeah ive searched that site and didnt really find anything

MTL_4runner

Checking for proper burn (ie why you would be rejetting your carb):
http://www.atvtime.com/ubb/Forum50/HTML/001233.html
http://www.rockymountainatv.org/pages/carb_jetting.htm

Rejetting is not that hard at all as long as you have easy access to the carbs themselves.

You need to look the the plug to see if rejetting will solve your problem though.

rngrchad

Alright man here goes:
If your 400 has any one or more of the following: aftermarket pipe/silencer/header/airbox/air filter then you will need to jet. When I was racing I carried a set of 3 sizes above stock main jets and 3 sizes below. I never used the smaller ones but when you get your 400's exhaust flowing better, it can burn more fuel. Thus you will need to jet up one or 2 sizes from stock. This jetting allows your carb to dump more fuel into the combustion chamber so the engine is not starving for it. Work your way in increments and find the jets that fit your bike the best. Depending on how much airflow you've gained over stock you may even need to go up more than 2 sizes. 75 percent of the time the problem lies within the main jet. Jets cost like 7 bucks a piece I believe. It's worth investing in many sizes.

jtm994

i have whites brother exhaust but the thing is i bought it with that on there i dont know if the carb was already jetted. and how hard would it be to rejet it my self?

rngrchad

jtm, the jetting is not difficult at all. Loosen rubber intake boot going into the carb, and loosen the rear boot leaving the carb. Twist the carb so you can access the bottom of the float bowl. I think it's a 17mm maybe an 18mm bolt on the bottom. Take it out and replace w/ new jet. It's that easy, I guarantee the bike probably still has stock jetting. Let me know if it works! Go up one jet size at a time and test drive each one. White brother's exhausts flow a lot better than oem.

.....I'm pretty sure I'm thinking of the 400ex carb....I may have just explained the 300ex carb. Not sure though.

jtm994

the jets how would i know which on to get. dont they come in different stages or something?