Please help with jetting!!!!????

[rangermike14]

Hey guys, Got a 2002 400ex supposedly bored 20 over?(previous owner said) The quad has a full FMF exhaust with a powerbomb header and a Hotcam. Just wondering what jets should be used. I dont think its jetted and it runs fine but having this aftermarket stuff makes me think it should have bigger jets. Any help would be greatly appreciated! Thanks guys, Mike

[400exrip]

I would run a 155 main and a 45 pilot.
Somewhere around there.

[rangermike14]

Sweet. What is stock?

[400exrip]

I think stock is 148 main and a 38 pilot

[rangermike14]

Also what would I have to do with the needle?

[400exrip]

Have the clip on the 3rd notch from top of needle if you are talking 99-04 400ex.

However on a 05 and up 400ex the needle is non adjustable and is already set up by the factory at the position of 3rd clip position.

[rangermike14]

Yes it is an 02. I have been looking around a little and it seems that alot of people are running a 170 main. Is that too big?

[400exrip]

You could try it but I would start out around 155-165 main. if it runs good with them then I would try the 170 main but if it bogs down in the top end or backfires a lot after you let off the gas then that 170 is to big, then just go back down some.

Because the main jet is you top end or high gear jet,and the pilot jet is your slow jet or bottom end jet, Now if you skip and sputter in the low gears you might have to play with that pilot jet, but I think 45 pilot should be great.

Jetting is a thing you have to test a lot to get it right. jetting works best on a dyno when you have all the readings and HP and top speed and RPM then you can really fine tune that thing.

Most people with 440's or 460's will run 170-180 mains. but with the smaller motors like 416's and 426's they will run 155-170 mains.

[rangermike14]

Ok cool. I appreciate the help. What about spark plug? Do I keep running the stock plug?

[400exrip]

Yep NGK DPR8Z is the stock plug keep on runnin it.

[honda400ex2003]

162 main, 38 pilot, and about 3.5 turns out on the f/a screw would get my vote to start out with. it is only an 85.5mm piston with a full exhaust, the cam wont make any difference in jetting.

good article on plug chopping and such:
http://www.exriders.com/vbb/showthread.php?s=&threadid=445695&highlight=jetting+placement

steve

[rangermike14]

All this being said....everyone's jets look to be different sizes. 155-165 is what I'm hearing and what brand jets are you guys talking? Thanks for all the help guys!

[honda400ex2003]

kiehin jets are what we are referring to. they are stock style jets.

dyno jet is different and would need the conversion chart to be recognized if not familiar with them

a 150 main keihin is equivalent to a 138 dj.

steve

[rangermike14]

Gotcha! Thanks!

[honda400ex2003]

not a problem

steve

[honda400ex2003]

how did it come out?

steve

[rangermike14]

Running 160 and 42. Is running good. It already had a 160 so just changed the pilot to a 42. Thanks again.