400ex jetting questions

[Zjx4]

Ok guys finally put a slip on on the 400ex, picked up a lexx mxe and I'm very happy what it. I also purchased a dynojet kit, unfortunately it didn't not come with pilot jets. Seems like everyone recommends a 40-42 pilot jet. My question is would that be a 40-42 keihin pilot jet? If so I will order those. As far as the dynojet kit, should I still use a dynojet main since I already have them or get rid of them and stick with keihin, not sure about mix matching jets. And either way which main jet size should I start with.

Low elevation 300-700 ft
Lexx mxe slip on
Uni filter
Airbox lid on due to lots of mud and water where I ride

Appreciate any help!

Also already pulled the carb and gave a a good cleaning since I decided to wait on rejetting til I have a little more info, I have no problem taking it off again to try out different jets

[rooster300ex]

Yes it would be a keihin pilot. I wouldn't worry about the pilot unless it pops on decel or it's really cold out and ur having problems starting it. Yes install the dyno jet jet kit and what it recommends. It should come with instructions. It should tell you what main with ur airbox lid on and what notch on the needle and how many turns out on the fuel screw. If the quad is popping on decel turn the fuel screw out alil at a time and see if it makes it stop. If it doesn't install the 40 or 42 pilot jet. After this is all said and done ride ur quad for awhile and check ur plug and see if its a dark cardboard color(perfect) If its black your running rich. Which means the jetting is off a bit. But if it runs good it won't hurt a thing. Hope this helped. There is also a BUNCH of info using the search feature on 400ex jetting.

[CJM]

I never had good luck with dyno jet stuff, their numbering system is vastly different and the sizes arent as accurate as they should be. I tried it on my 400 cause all my friends used it and I wound up with a 190 (something like a 200 keihin I think) and it ran but not well and once I went back to keihin and put a 170 in there it ran so much better and had alot more power.

You should be able to get away with a 40-42 pilot and a 150-160 main. Id start with a 155 keihin main and see how it runs. YOur really giving up a good bit of power keeping the airbox lid on.

[kt1148]

You can do the airbox lid mod with an Outerwears pre-filter like I had. It kept the mud and water out(water would just beed up on top of it)
I also removed the plug at the bottom of the airbox in case any water were to get in.
1718108313

[CJM]

You can do the airbox lid mod with an Outerwears pre-filter like I had. It kept the mud and water out(water would just beed up on top of it)
I also removed the plug at the bottom of the airbox in case any water were to get in.
1718108313

Yes, very good idea! I also had this done on my 400 and I removed the snorkel and plugged the hole with a spray paint can cap. Worked great. Im not sure how much water you ride in OP, but the more you mud bog with this sort of machine the worse things wear. Carrier bearings will be the worst of it along with the swingarm bolt.

[Zjx4]

Thanks guys I will look into the outerwears pre filter, also plan on grinding down header welds when I take it to wrap. I'll put in the recommended dynojet main jet and see how it runs. If need be I will order some keihin pilot jets.

[Zjx4]

Yes, very good idea! I also had this done on my 400 and I removed the snorkel and plugged the hole with a spray paint can cap. Worked great. Im not sure how much water you ride in OP, but the more you mud bog with this sort of machine the worse things wear. Carrier bearings will be the worst of it along with the swingarm bolt.

Not like I go out of my way to get wet just some small stream crossings in the trails. And no mud bogging, also just random muddy ruts along the trails. Picked up the quad for a pretty good price for its condition needed absolutely nothing, just now getting all the little things out of the way (routine maintenance) next it probably a chain and sprocket set, they are a bit worn and I'm considering a 39t rear sprocket to pick up a little bit of torque in the woods

[CJM]

Primary drive chain and sprocket, Ive run every brand oyu can think of and they are the best bang for the buck and hold up very well.

The outerwears lid will work well, water will not go in unless you really swamp it.

[Zjx4]

Primary drive chain and sprocket, Ive run every brand oyu can think of and they are the best bang for the buck and hold up very well.

The outerwears lid will work well, water will not go in unless you really swamp it.

Thanks I will probably order a set once I get the jetting straightened out

[Stickman400]

If you wanna spend the extra dough pick up the D.I.D./J.T. Steel combo. It lasts forever and wears/stretches slow so you don't need to adjust the chain nearly as much. I used to run the Primary Drive combo, but ran the aluminum sprockets (dumbest thing ever) and they just didn't last for nothing. Decided to get the DID/JT combo and I'm still running the ones I bought 4 years ago now. Adjusted it maybe 2 or 3 times so far. Lots of life left in them.

[Zjx4]

So I went ahead and out in the dynojet 146 main, starts,idles, and runs good...only thing is if it's at idle and I mash the throttle, it will bog/shutoff, no backfiring popping or sputtering when letting off the throttle and as soon as I start moving I can mash it all I want, so just from idle to WOT it will bog.
pilot jet is still stock 38 left needle alone and air/fuel exactly 3.5 turns out...any suggestions?

[CJM]

Too rich on the main, dynojet 146=160 keihin jet. Air fuel screw is out to far, will fall out. Go up one side to a 40 pilot. Try a 152 keihin main

[Stickman400]

Drop the clip on the needle 1 notch. I had a similar problem with my stock 400 carb. when I had one on mine before I swapped to the 450 carb. I dropped it from the 3rd notch to the 4th and it cured all my problems.