01 400ex jeting tips

[brandon86]

I'm all stock except for a big gun slip on and a K&N air filter with no air box.
I need to rejet what size would you start out trying??

[atvhonda-rider]

just depends really, whats your elevation? if you're not too high up try a 152 mj or a 160 and go from there, i hada slip-on CT racing a year ago and they suggested a 160, but now i have my full system HMF i run a 152. id say start with 160 and experiment around, if its popping and or various smoking, you need to rejet

[400exrider707]

Just doing a main jet change wont get the full effect.


I would start with this and go from there...

155 main
42 pilot
needle on the 4th clip down from the top
fuel screw 2 1/4 turns out.


Then do a plug reading.

[atvhonda-rider]

right, but i like to start with the main jet, then dial it in from there

[400exrider707]

Originally posted by atvhonda-rider
right, but i like to start with the main jet, then dial it in from there


doesn't matter where you start, why not do all of the jets at once so you dont have to take the carb off so many times?

[400exstud]

His reasoning of starting with the main jet comes from science experiments. You must only change one variable to understand what is happening.

If you change all of them at the same time they may interfer with each other and give really messed up results. If you are really good with carbs you may be able to tell if your needle is too rich and main is right on, but if he was that good he wouldn't need our help.

It is easiest to dial in the main, and then try the needle. Finally the pilot.

[400exrider707]

What's your point, you still dial them in individually whether they are all in there or not.... Each jet only covers a certain part of throttle openings, so it doesn't matter if you put them all in at once or do one at a time, you still only test each one at a time. Also if you dont change them all at once you are more likely to get messed up results from it not running correctly on different circuits, and if he's not that good with carbs he probably doesn't know which jet to change if its acting up at a certain throttle opening so changing them all at once would be much more beneficial to him.

brandon86 - It's up to you man do what you want, you have enough info to go on, any more questions, just ask.;)

[400exstud]

Originally posted by 400exrider707
Each jet only covers a certain part of throttle openings, so it doesn't matter if you put them all in at once or do one at a time,

Yes and no.

While each jetting circuit has its general range that we all know of there is significant overlapping between the circuits. This gray area where the overlapping occurs could cause a lot of confusion to a person who is new to carbs.

If you change one thing at a time you know either...
1. that was the right thing to do. Perhaps I should go even farther in that direction

2. that was the wrong thing to do. I have to go the other direction.

If you change more than one thing and get a messed up result you may be confused as to what actually caused the result. Maybe both changes were wrong. Maybe one. Which one? Breaking it down to each jetting circuit just simplifies things for the first timer.

[atvhonda-rider]

That was kind of my point i was trying to get at, thank you 400exstud. I dont know all about carbs but i know enough, to where when i re-jet, i start with the main jet, and go from there. And being a first timer on carbs myself, i figured i'd give my advice that helped me when i started... just tryin to help, sorry!