jetting 400ex

[400ex4rick]

adding yoshimura slip on, sparks cdi and k&n filter everything else is stock. i was told to just change main jet to a 165 also told main jet to a 155 and pilot to a 42?? anyone have similar set up point me in right direction????

[phebus]

I just got mine dialed in. I'm running a 155main, 40 pilot w/ 2 1/2 turns out on the screw. Needle clip in the stock position. K&N filter w/lid off, White Bros. e-series slip on pipe.

This is at approx. 500' elev., air temp. 50-60*. I have a friend running the same way, so I copied his jetting. I tried with a 152 main, and a 158 main, and this seems like the best.

By the way, this is with Keihin jets.

[AtvMxRider]

I would go with 160 main and 42 pilot. Thats what I run in mine and have had zero problems.

[chrisp333]

155 main is prob good and there is nothing wrong with a 40 pilot. sounds good to me.

[400ex4rick]

thanks guys anyone have any info on just putting in 165 main???????

[JP400ex]

Hey Chrisp333, I've got a similar setup to you! Im getting real close to having my jetting good finally. When i got the bike the guy had a 200 main jet in it with a stock pilot. I now have a 168 main / 42 pilot and i moved my needle down to the 4th position. I still get some lean popping at about 1/4 - 1/2 throttle so im thinking im going to move the clip all the way down for winter and move back up to 4th for the summer. As for the main jet, it seems to be running pretty good on top end now, i may still try to go down to a 162 though.

[phebus]

It sure seems to me that people tend to jet way rich. Sure, if you're a little rich, your quad will run good, but for maximum power, you need to be jetted right. There is way to much fear of melting down by running too lean, so people don't take the time to read plugs, or develop a feel for what the engine is doing. It isn't black magic or voodoo, take the time to learn!! Just my .02

[cals400ex]

Originally posted by 400ex4rick
thanks guys anyone have any info on just putting in 165 main???????

my info for that is put in a smaller jet. a keihin 155 should do wonders for you.