jetting 400ex

[dunnp650]

new here bought daughter a 01 400ex it has a procicut pipe and I am putting a quite core in and it has a kn air filter with outerwear I am wanting to know if I should put 42 pilot jet in for starting and what size main jett

[Aceman]

Jetting depends on temp, elevation, etc. and you didn't mention any of it. When you purchase a pipe there is usually a MJ size they will recommend for you. But as far as a Pilot Jet, 42 should work for you. Take a look at the jetting article in FAQ forum.

[Maxxed out]

My friend has the same mods as you and he is running a 155mj.. but he doesnt have the quiet core, so you might want to try a smaller mj than 155 because of that [quietcore].. but like aceman said, temp. and elevation also play a pretty important role in jetting..

[zephead400ex]

Originally posted by Aceman
Take a look at the jetting article in FAQ forum.

that would be a good place to start

btw: welcome to EXriders!

good luck

[BBW]

Do a search on jetting and you will get several hundred returns with everything from leaving it the way it is to a 172 main. You just need to sort out the good the bad and the ugly.