Jetting a 400ex

[blacklabel117]

ya man the motor was running fine i never did check the plug but wat i was confused about was that ne thing bigger than the 148 it was like studdering rly bad uk so idk man nd i will have to buy a new plug for it to check

[f4iracer]

What's the best place to find a shim washer for these newer 400ex's? My needle is not adjustable.

I'm running a uni filter with a slipon and all i have right now is just a 152 main and stock pilot.

Starting it is ****ty so i'm going to put a 40 or 42 pilot in, what do u guys think?

Also, i'm gonna try a 155 main, i think it's lean since i've done the air filter mod. It was jetted pretty good with just the slipon before i put the uni in, but now i need more.

[f4iracer]

it's amazing how so many people on this forum just read the posts and don't reply.

considering that many people have shimmed their needles i'm wondering why i haven't got a reply as to what size washers they need?


blacklabel it sounds like all you need to do is back your pilot screw out about a half turn.

I had to learn the hard way because i wasn't informed! Basically if you up on the main or the pilot jet you're gonna have to back out the a/f screw.

Not many people mention this because the a/f screw is for fine tuning. Well, i got mine jetted with a slip-on and air filter and i've got the 40 pilot and the 152 main, and it was stumbling when i would hold the throttle on steady idle at a lower rpm.

All i needed to do was back out the pilot screw about a half turn. Runs perfect right now.

Basically if you go up on the main or pilot jets you're gonna have to turn your a/f screw out! it goes right along with changing the jets.

[thinkfaster]

Just put on a full white bros. e series and ended up with a 155 main and i went ahead and installed a 40 pilot to help with hard starting...this was my first time jetting and it wasnt really hard, just time consuming. My advice to the newbies: read ALL the write ups you can find! they were a huge help! i couldnt have been happier to see that cardboard colored electrode!

[trx400exrider14]

I have a 2004 400ex and i am wanting to buy a hmf slip on exhaust with K&N air filter.What should my main and pilot jets be set to? Or if i get a slip on do i need to jet my carb?

[dirtrider77]

Originally posted by trx400exrider14
I have a 2004 400ex and i am wanting to buy a hmf slip on exhaust with K&N air filter.What should my main and pilot jets be set to? Or if i get a slip on do i need to jet my carb?

Put a 42 pilot in it regardless

If you just put a slip on use a 165 or 170 main...start with 170 and if needed go to 165

Buy this:

http://hmfracing.com/shop/performanc...0ex-99-10-jets