99-03 Vs 04-present Jetting???

[NrCalDuner]

I have been doing alot of researching and have found that the jetting recommendations from alot of people on here are different, and not just because of elevation. Are the older carbs different, and take bigger jets when you mod them? I am getting ready to put a HMF slip on with a K&N and no lid on my wifes 2006 400ex and want to get the jets right the first time. I already have the 04 adjustable needle and 155, 160 mains, and 42 pilot. We live about 100' above sea level, so I was thinking the 160 main. The hmf website says a 152, but I don't know if that is with the lid on or off. So can someone lead me in the right direction. Thanks!

i am wondering the same thing and I called HMF today and this is how it went.

"Yes I am looking to jet my 2004 400ex it has the HMF slip on, K&N air filter, and the lid is removed. What jets would you recomend?"

"Well the 400ex we dynoed we used a 42 pilot and 152 main, a free flowing filter and the lid removed."

So my pint is what is the "free flowing" filter? They wouldnt say and I asked about with my K&N and they just said we used a "free-flowing filter" so I dont think it was with a K&N otherwise I think they would have said. To me a 152 seems to small and I think for an HMF, K&N with the airbox lid removed at about sea level I think a 155 would do the trick.

[NrCalDuner]

Anybody else?

[CarGuy7a]

IMO i would consider any performance filter such as K&N, uni, etc.... as a "free flowing filter" because they flow more than just a regular stock filter.

usually a 155 jet is what i've seen most aftermarket pipe companies suggest as a jetting after doing the pipe and filter mods. this is usually just a recommendation for a starting point due to different elevations and such. the fine tuning is up to you.

my buddy has an 03 and mine is an 04 and i've done the jetting on both and there is virtually no differences to the carbs that i've seen with the naked eye.

the older carbs may be slightly different but not enough to notice.

[Pipeless416]

what he said. the filter will not make as much of a difference as things like temperature and elevation will. i would also consider a "free flowing filter" anything but stock. when i had a stock carb, i ran a 160k main, 42 pilot, needle clip one below stock, and 2.5 turns out on the fuel screw. that was for about 720 ft above see level, and temps from like 20-90. during the winter i just ran with the lid on to richen it up. try the 160 first and see how it runs. that should be really close.