Do you have to Re-jet?

[03400EX14]

Just got a new 400ex and ordered a K & N with an outerware. I was told if I put it on I would have to Re-jet. Is that correct.
Thanks.

[Str8Wicked]

I didn't re jet on mine with a K&N and open airbox. I did re jet thou after I put on the slip on pipe.

[Doibugu2]

When put mine on, I also bought the dyno jet kit. I actually was running a little rich and installed the 142 dyno jet. I did notice a little better throttle response. When I installed the K&N, I did not notice any change in the bike.

Also, realize everyone is at a different elevation, so like str8wicked was able to put the filter on and take his airbox lid off without rejetting. I don't think we could do that, but I am just guessing, being that we are at similar elevations.

[JB's 400ex]

I would suggest rejetting. It will help with performance but it probably depends on your location(altitude, temperature, humidity, etc.) That is also what you pay all that extra money for the jet kit for is a bunch of $4 dollar jets. Correct me if I am wrong but to some extent, more air + more fuel = more power. Within reason of course.

[RiPPiNiTuP7]

Either way I would check the jetting...it only takes a few minutes...

[cals400ex]

by just putting on the filter you won't notice any gain. my friend had one with out jetting and i was just as quick as him throughout the entire power range. he then rejetted and his made some more power. jetting is critical if you want all out performance. by changing filters, making airbox mods, adding pipes, or even temp changes make the jetting change. i actually change to a bigger main jet as the winter months come.

[tom400ex]

ok I've been reading and thinking about re-jetting for a little bit now and my question is.
How do you know what to re-jet to or what is the propper setting?:confused:

[Steve-o 400EX]

You have to check ur plug and see if ur rich or lean. Depending on how white or black the inside of the plug is, thats how you determine it. For just the filter i would only go to a 150 main and a 40 pilot max. If you get a pipe i would take it to 152 and 42. But this will vary depending on your elevation and riding conditions.

[Newbie400ex]

I got a K&N filter and Dynojet kit all together. I first put the filter on and rejetted to a DJ142 which is what Dynojet and K&N recommended. I really didn't notice much power gain. I bought a WB e-series the other day and put that on. Made some difference in power and made it run pretty lean. (plug check). So today I said what the heck I'll go ahead and pull the airbox lid and rejet up to a DJ170.(which is what Dynojet recommends for that setup) Whoah!! It blew me away! It is way better. The difference is pretty good especially in the mid-to near top end. I also did the jet change with the carb on the bike. All you need is a 17mm combination wrench and a stubby screwdriver and whammo... Screw removing the carb.;)

[Yoshi400ex]

what if u had a K&N and a slip on what size jets..

[cals400ex]

with a KandN and a slip on i would say around a 155 keihin main jet. this is just a guess because the brand of pipe and the temp. outside are major factors with jetting. this is also assuming you don't have any airbox mods. remember that keihin and dynojet have different numbering techniques. a 150 keihin does not equal a 150 dynojet.

[Yoshi400ex]

were can i order these goodies??

[lol]

u got a another quad

[JOEX]

Go to your local cycle shop...they should have the jets you need.

Joe

[Martin Blair]

I would re-jet to get all the avalible power out of ur engine. I am getting a jet kit, it works fine on my rancher. but i dont know how it will work on the 400 i will probably get some new jets that Tom and TC racing recomends when i get my pipe.

[SmokinJoe@PJR]

I had a T-4 and k&N filter in stock closed box and stock motor and ended up with a 156 main and raised needle 1 notch