07 400ex jetting questions

[xd-shawn]

hey guys, new guy here, just got a 07 400ex a few weeks ago and i'm already thinking about picking up some parts for it, i'm planning on getting a HMF slip on pipe and a K&N filter for now, i'm not gonna mod the airbox or anything like that being that it is gonna be used only on trails

so my question is, what jets?

i've done some searching around and from what I see mabye a 40 pilot and a 155 main? this thing runs like crap in this cold weather, wont idle very good ect, i'm just looking for a little more power, good sound, and reliability, that's why i got the 400ex to begin with (reliability) i dont need every last HP out of it and i'd rather it be a little rich/safe than lean

i'm located in NW ohio for those that will ask about elevation

thanks for any help!! i'm new to the whole 4wheeler world

[casey_lamm]

if you are truely going to jet it right I would start with a 170 and work your way down.(if running no air box lid) Otherwise I would try a 150 and go down to around a 142. I had those mods at one time as my only mods and I ran a 40/142 or 145 i think you will be pretty close I would bet. I later change my pilot to a 42 to help starting in winter. If you are at stock 38, might as well do the 42 pilot now. It wont hurt and you are buying a jet anyway.

btw...i think the k&N POWER KIT includes dynojets. you would have to still get the pilot jet seperate.

disclaimer all jet sizes i mentioned were Dynojets except the pilot.

There is a conversion chart floating around that shows you what a DJ#'s i listed about translate into for the stock jet brand(keinen sp?).


Originally posted by xd-shawn
hey guys, new guy here, just got a 07 400ex a few weeks ago and i'm already thinking about picking up some parts for it, i'm planning on getting a HMF slip on pipe and a K&N filter for now, i'm not gonna mod the airbox or anything like that being that it is gonna be used only on trails

so my question is, what jets?

i've done some searching around and from what I see mabye a 40 pilot and a 155 main? this thing runs like crap in this cold weather, wont idle very good ect, i'm just looking for a little more power, good sound, and reliability, that's why i got the 400ex to begin with (reliability) i dont need every last HP out of it and i'd rather it be a little rich/safe than lean

i'm located in NW ohio for those that will ask about elevation

thanks for any help!! i'm new to the whole 4wheeler world

[xd-shawn]

isn't a 142 or 145 gonna be leaner than stock? i thought stock was 148?

you'll have to forgive my ignorence when it comes to this stuff i'm still learning alot, when i get jets i'll be buying them direct from my honda dealer probably


i also forgot to ask, any advise on where to set the mixture screw?

basically i'm asking, what do i need to do to my 400ex to support a HMF slip on pipe and a K&N filter, the airbox lid is staying on

[08400EX]

Originally posted by casey_lamm

btw...i think the k&N POWER KIT includes dynojets. you would have to still get the pilot jet seperate.

disclaimer all jet sizes i mentioned were Dynojets except the pilot.



Be careful with the jet sizes K&N sends with some of their kits. When I got my PowerLid they sent 168 and 170 Keihin jets (not Dynojet) way to rich for my 08.

It seems there is also a big difference in jet recomendations depending on the year model. If I recall most places I saw showed the early 99-03 using a much larger main jet than the 04-up. I assume it is because of the carb change in 04?

For example HMF recommends the following...

Honda 400EX:
1999 - 2003 Slip on:
165/170 Keihin Hex

Honda 400EX:
1999 - 2003 Full System:
180/200 Keihin Hex

Honda 400EX:
2004-> Full System & Slip On:
152 Keihin Hex / 42 Pilot

[casey_lamm]

i was refering to a dynojet and it was a 148 that i had.

I used these instuctions when setting up the jetting and found they were pretty close..you might use them as a starting point as well if you chose the dynojet kit.

as to you statement about being leaner. i think dynojets tend to run a little different then others. I think a 148DJ is equal to a larger size of the others. I will try to find the coversion chart.

"STAGE ONE INSTRUCTIONS
1. Remove top carb plate. Remove the slide lift arm screw and the two
needle plate screws. Flip the linkage forward and remove the slide
(Fig. A).
2. Install Dynojet needle on groove# 3 for applications below 5000 feet,
groove #2 for above 5000 feet, using all stock spacers. Install the Dynojet
washer above the E-clip.
3. Remove stock main jet. Replace with the Dynojet Main Jet Adapter
(DJA001). Screw the Dynojet main jet provided into the Main Jet Adapter.
If you are running the stock exhaust use the DJ142 below 3000 feet,
DJ138 from 3000 to 6000 feet and DJ134 above 6000 feet. If you are
running an aftermarket exhaust, use the DJ146 below 3000 feet, DJ142
from 3000 to 6000 feet and DJ138 above 6000 feet. Be sure that the jet
you are changing is the main jet.
4. Locate the Fuel Mixture Screw (Fig.B). For 2005 models ONLY use the
tool provided (DT008) to adjust the mixture screw. For 1999-2004
models, use a flat blade screwdriver. Turn the mixture screw clockwise
until it seats, then turn out 3.5 turns below 5000 feet or 3 above 5000 feet."

That is from dynojets website.


if you look at dynojets website
Originally posted by xd-shawn
isn't a 142 or 145 gonna be leaner than stock? i thought stock was 148?

you'll have to forgive my ignorence when it comes to this stuff i'm still learning alot, when i get jets i'll be buying them direct from my honda dealer probably


i also forgot to ask, any advise on where to set the mixture screw?

basically i'm asking, what do i need to do to my 400ex to support a HMF slip on pipe and a K&N filter, the airbox lid is staying on

I saved this into a word document to help myself and others when questions about jetting are asked.
jet sizing chart


Width------Keihin # -- DynoJets # -- Mikuni #
0.0350---- 92.5--------- 92----------- 86.3
0.0360---- 95----------- 94----------- 88.1
0.0370---- 97.5--------- 96----------- 90.0
0.0380---- 100---------- 98----------- 91.9
0.0390---- 102.5------- 100---------- 93.8
0.0400---- 105--------- 102---------- 95.6
0.0410---- 107.5------- 104---------- 97.5
0.0420---- 110--------- 106---------- 99.4
0.0430---- 112.5------- 108--------- 101.3
0.0440---- 115--------- 110--------- 103.1
0.0450---- 117.5------- 112--------- 105.0
0.0460---- 120--------- 114--------- 106.9
0.0470---- 122.5------- 116--------- 108.8
0.0480---- 125--------- 118--------- 110.6
0.0490---- 127.5------- 120--------- 112.5
0.0500---- 130--------- 122--------- 114.4
0.0510---- 132.5------- 124--------- 116.3
0.0520---- 135--------- 126--------- 118.1
0.0530---- 137.5------- 128--------- 120.0
0.0540---- 140--------- 130--------- 121.9
0.0550---- 142.5------- 132--------- 123.8
0.0560---- 145--------- 134--------- 125.6
0.0570---- 147.5------- 136--------- 127.5
0.0580---- 150--------- 138--------- 129.4
0.0590---- 152.5------- 140--------- 131.3
0.0600---- 155--------- 142--------- 133.1
0.0610---- 157.5------- 144--------- 135.0
0.0620---- 160--------- 146--------- 136.9
0.0630---- 162.5------- 148--------- 138.8
0.0640---- 165--------- 150--------- 140.6
0.0650---- 167.5------- 152--------- 142.5
0.0660---- 170--------- 154--------- 144.4
0.0670---- 172.5------- 156--------- 146.3
0.0680---- 175--------- 158--------- 148.1
0.0690---- 177.5------- 160--------- 150.0
0.0700---- 180--------- 162--------- 151.9
0.0710---- 182.5------- 164--------- 153.8
0.0720---- 185--------- 166--------- 155.6
0.0730---- 187.5------- 168--------- 157.5
0.0740---- 190--------- 170--------- 159.4
0.0750---- 192.5------- 172--------- 161.3
0.0760---- 195--------- 174--------- 163.1
0.0770---- 197.5------- 176--------- 165.0
0.0780---- 200--------- 178--------- 166.9
0.0790---- 202.5------- 180--------- 168.8
0.0800---- 205--------- 182--------- 170.6
0.0810---- 207.5------- 184--------- 172.5
0.0820---- 210--------- 186--------- 174.4
0.0830---- 212.5------- 188--------- 176.3
0.0840---- 215--------- 190--------- 178.1
0.0850---- 217.5------- 192--------- 180.0
0.0860---- 220--------- 194--------- 181.9
0.0870---- 222.5------- 196--------- 183.7
0.0880---- 225--------- 198--------- 185.6
0.0890---- 227.5------- 200--------- 187.5

[STUNTIN400EX]

great chart foxhondarider just saved it to word myself.