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2006 400ex Long distance troubleshooting

Josh this is a long distance troubleshoot . I bought a 2006 Honda 400ex down in Baja ( I am still in the U.S). It has a Procircuit T4 pipe,not sure of the airbox. My buddy that picked it up for me said it idled very poorly,popping etc. But runs great out of the idle circuit. So I am thinking it is most likely lean,trying to get together some parts before I head down next month. After reading this GREAT thread I am thinking I need to install a 42 Pilot,and a 170 main ,install a fresh Plug and see how it acts . Does this sound like a good plan to you ? Also where do you recommend ordering the Jets from,and what brand ? Thanks ! Great forum here :hail:
 

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Ok, so here's one for you. I have an 03 400ex with a 440 kit, hotcams stage 2, k&n with no air box lid, slip on, a new 05 carb rejetted to a 180 dynojet main, dynojet needle on 3rd clip, and pilot screw at 3 turns. Seemed a bit rich/boggy at a 185 main jet. Altitude is sea level. And it's only a 10.5:1 piston. Extra oil cooler/high capacity cool through tank for temp issues. Runs good but has slight stumble in throttle on hard acceleration. Do you have any suggestions on jetting that might help?
 

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And yeah, I intend on doing a plug chop as soon as I have the time. I live in Alaska and the lake I live on is frozen and rideable so I just need to find the time. And the needle jet runs to 2/3 or 3/4 throttle? Thanks for the help in advance.
 

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I have a 2005 trx450r I'm gona do a dasa full exhaust and a moflow on my airbox so it breaths better do you have any suggestions on what I should do with the main jet and slow jet i was thinking 180 on main and a rough estimate on how many turns out I should put pilot screw
 

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Greetings, everyone. This is my first forum post. I just recently purchased a 2005 400EX which came with a White Brothers slip-on. Supposedly, the top end of the motor was recently redone with a 440 big bore (however I'm unsure how to verify this w/o tearing the motor down).

I recently removed the carb to ascertain what jetting was being ran. The stock 38 Keihin pilot jet was installed, and a 165 Dynojet main jet (equivilent to ~184 Keihin jet sizing according to a chart that I referenced).

I purchased an assortment of main jets ranging from 160-190 as well as a 40 and 42 pilot jet. I'll most likely run the 42 pilot jet. The bike seemed to run fine with the 165 Dynojet main and slip-on, however I'm thinking I'll want to increase the main jetting to compensate for a Uni filter and EHS airbox lid that I recently ordered.

Could anyone recommend a good starting point regarding my jetting assuming installation of the filter and airbox lid? I'll probably also grind down the welds inside the factory exhaust manifold in the near future as well, but will probably wait until the next oil change as it seems the oil tank will need to be drained / removed to remove the manifold.

I understand being unable to verify the big bore setup can drastically complicate choosing the proper jets. Just trying to see if I can get some guidance regarding a starting point. I plan on performing some plug chops once it's all up and running to try to dial things in further. My elevation is ~2200ft above sea level. I probably won't ride much below that but may potentially ride a couple thousand feet above that, depending on where the trails take me.

Thanks in advance to anyone who can offer any input regarding my jetting situation!
 

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hi guys, im new to the page and i was woundering. i have an 02 400ex that is running hot and need info.

when i ride i put my hand on the end of my exhaust to fill it and its really hot to were i cant touch it even if i ride for 5 min.

i have a uni filter and a white brothers slip on, what can i do?? thanks for the help
 

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i have a 2003 trx 400ex with a lexx exhaust with no baffle and no snorkel on the air box.also i have a stage 1 hot cam installed. my elevation is 676 ft. for the jet i have the stock 148 that came in a rebuild kit and the fuel adjustment screw is at 3 turns out. when i pin the throttle anytime and let off a little bit it will shoot a flame out the exhuast and pop
 

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Jetting 1992 Honda 250x

I have a Honda 250 X I am at 700 feet altitude and have a 128 Main jet i'm bogging out half throttle i'm wondering what size jetting slow jet and pilot jet I should use I am running a DG exhaust thank you in advance nice thread man
 

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07 trx400 engine stock, Lexx pipe, k&n airbox cover, new OE Honda carb, unaltered. Bogs on instantaneous wide open throttle. Responds immediately if first notch of choke is left on. Otherwise plenty of power. Tips on jetting to start with?. Also what about accelerator pump bleed, hear that can affect WOT response
 

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Stock 400ex carbs dont have an adjustable leak jet. The only adjustment that can be made to accelerator pump is shortening the push rod or lengthening it to adjust when it comes in. But honestly the 400ex carb is such a limited carb in flow anyway its kinda pointless to fine tune the AP at all. Round slide carbs arent able to have that kind of throttle response. With all your mods and elevation i would start around a 170-175 main jet and put a 42 pilot jet in it. Dropping the clip one slot will also help alot with mid power range but the 05+ carbs dont have an adjustable needle. Pick up a rebuild kit for an older 400ex pre-05 and it will come with an adjustable needle. Go one slot down from middle.(fat part being top and skinny being bottom). Also get rid of that stupid D shaped mixture screw. The same kit will come with a flat tip head one to replace it with. Take that screw in to very lightly seated. Then turn it out around 2 1/4---2 1/2 turns. Should have a whole different quad after following these directions. Welcome to the forums!
 

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Before you do anything click the link below and follow the instructions to download a manual for your quad
Honda Manuals

Alright . . . here it is for the people that always have questions about this subject. I have been thanking about writing one up for awhile but haven't got around to it. So here we go. . .

Jetting in quads is a neccesity even when you buy a new quad and plan on riding it hard its best to go ahead and upgrade to a little larger jet.

Since I own and race a 400EX that is what I am going to be using as my example.

Factory jetting is 148 main jet with 38 pilot and 2 turns out on the air/fuel screw. This is actually a little lean for EPA standards so Honda looks good. First thing to do is atleast bump the main jet up to a 155.

Here is a Diagram to show what I am talking about.
Key:
For 400EX 99-04
Pilot jet-slow jet
air/fuel screw-pilot screw​




Key:
For 400EX 05-09​




Now when adding performance parts to a quad that increases airflow to the motor and out the motor REQUIRES more fuel. The jet sizes depends on the parts added and the brand of parts. For ex. a K&N air filter requires a bigger jet than a UNI filter because its a higher flow filter.

Signs that your jetting is wrong:
-header glows red, backfire on deceleration, plug is a white color, quad gets hot very quick -- these are signs that your jetting is to small and you need larger main jet and you might need to run your pilot screw 1/4 turn out
-bogs on acceleration, hard to start, plug is a dark brown color, quad doesn't feel like its at its full potential -- these are signs that your jetting is to big and you might need to turn your pilot screw in a 1/4 turn or more

To check plug color you have to fire up your quad let idle till its warm or ride it till its warm then take it on a decent size stretch and go full throttle in 4 or 5 most will tell you 5 but it really doesn't matter as long as your motor hits max rpm. As soon as its at the time to shift pull the clutch in and kill the motor. Then coast back to your house or stop on the side of the road and pull your plug out. If its a nice tan color then your good. If its a dark brown or black color your to rich or if its a white or light grey your to lean. The end of your spark plug is what matters on the very bottom(the L part). If you have a white color or dark brown color in the middle of the L bend then your pilot screw is off.

Depending on your altitude and the size of your pilot jet/slow jet determines the size of main jet you should use.
For quads with no motor work, a slip on and filter (main application for everyone on here)
These are for stock slow jet of 38 (for slow jet of 42 take off 5 main jet sizes)
(for 450R's take between 10 to 15 sizes off of the main jets of the 400EX)

Cross Reference of Jet Sizes

ALTITUDE IN FT.
400EX
(Factory main jet #148)
altitude below 1000
main jet 175 to 185
pilot screw 2 1/2 to 3 turns out

altitude between 1000 to 2500
main jet 165 to 175
pilot screw 2 1/4 to 2 3/4

altitude between 2500 to 5000
main jet 155 to 165
pilot screw at stock

300EX
(Factory main jet #122)
altitude below 1000
main jet 145 to 155
pilot screw 2 1/2 to 3 turns out

altitude between 1000 to 2500
main jet 135 to 145
pilot screw 2 1/4 to 2 3/4

altitude between 2500 to 5000
main jet 125 to 135
pilot screw at stock​

Now if you plan on doing more that requires more fuel. A hotter spark plug requires bigger jet as well. For those who ride in dunes need to be 5 bigger on there main jet from the altitude listing above. For those of you who have changed your slow/pilot jet up to a 40 or 42 your jetting will be on the lower end of the main jet sizes listed above.

For machines that have extensive mods you can leave me a message on my profile. This is for people with motor work and head work that needs more attention to detail with jetting.

Remember this is just a starting point and every quad is different this is just to help us keep from having to answer the same questions all the time.

For questions on utility quads ask helmut or one of the other guys that are good in that area for snorkeling and other mods.

If you have suggestions on anything that you thank should be different just write it below andTHANK
Before you do anything click the link below and follow the instructions to download a manual for your quad
Honda Manuals

Alright . . . here it is for the people that always have questions about this subject. I have been thanking about writing one up for awhile but haven't got around to it. So here we go. . .

Jetting in quads is a neccesity even when you buy a new quad and plan on riding it hard its best to go ahead and upgrade to a little larger jet.

Since I own and race a 400EX that is what I am going to be using as my example.

Factory jetting is 148 main jet with 38 pilot and 2 turns out on the air/fuel screw. This is actually a little lean for EPA standards so Honda looks good. First thing to do is atleast bump the main jet up to a 155.

Here is a Diagram to show what I am talking about.
Key:
For 400EX 99-04
Pilot jet-slow jet
air/fuel screw-pilot screw​




Key:
For 400EX 05-09​




Now when adding performance parts to a quad that increases airflow to the motor and out the motor REQUIRES more fuel. The jet sizes depends on the parts added and the brand of parts. For ex. a K&N air filter requires a bigger jet than a UNI filter because its a higher flow filter.

Signs that your jetting is wrong:
-header glows red, backfire on deceleration, plug is a white color, quad gets hot very quick -- these are signs that your jetting is to small and you need larger main jet and you might need to run your pilot screw 1/4 turn out
-bogs on acceleration, hard to start, plug is a dark brown color, quad doesn't feel like its at its full potential -- these are signs that your jetting is to big and you might need to turn your pilot screw in a 1/4 turn or more

To check plug color you have to fire up your quad let idle till its warm or ride it till its warm then take it on a decent size stretch and go full throttle in 4 or 5 most will tell you 5 but it really doesn't matter as long as your motor hits max rpm. As soon as its at the time to shift pull the clutch in and kill the motor. Then coast back to your house or stop on the side of the road and pull your plug out. If its a nice tan color then your good. If its a dark brown or black color your to rich or if its a white or light grey your to lean. The end of your spark plug is what matters on the very bottom(the L part). If you have a white color or dark brown color in the middle of the L bend then your pilot screw is off.

Depending on your altitude and the size of your pilot jet/slow jet determines the size of main jet you should use.
For quads with no motor work, a slip on and filter (main application for everyone on here)
These are for stock slow jet of 38 (for slow jet of 42 take off 5 main jet sizes)
(for 450R's take between 10 to 15 sizes off of the main jets of the 400EX)

Cross Reference of Jet Sizes

ALTITUDE IN FT.
400EX
(Factory main jet #148)
altitude below 1000
main jet 175 to 185
pilot screw 2 1/2 to 3 turns out

altitude between 1000 to 2500
main jet 165 to 175
pilot screw 2 1/4 to 2 3/4

altitude between 2500 to 5000
main jet 155 to 165
pilot screw at stock

300EX
(Factory main jet #122)
altitude below 1000
main jet 145 to 155
pilot screw 2 1/2 to 3 turns out

altitude between 1000 to 2500
main jet 135 to 145
pilot screw 2 1/4 to 2 3/4

altitude between 2500 to 5000
main jet 125 to 135
pilot screw at stock​

Now if you plan on doing more that requires more fuel. A hotter spark plug requires bigger jet as well. For those who ride in dunes need to be 5 bigger on there main jet from the altitude listing above. For those of you who have changed your slow/pilot jet up to a 40 or 42 your jetting will be on the lower end of the main jet sizes listed above.

For machines that have extensive mods you can leave me a message on my profile. This is for people with motor work and head work that needs more attention to detail with jetting.

Remember this is just a starting point and every quad is different this is just to help us keep from having to answer the same questions all the time.

For questions on utility quads ask helmut or one of the other guys that are good in that area for snorkeling and other mods.

If you have suggestions on anything that you thank should be different just write it below and ill fix it.

THANKS AND I HOPE THIS HELPS NEW MEMBERS!!!!!!!!
I have a 400ex 416 build with 11:1 weisco piston, stage one hot cam, slip on pro circuit t4, k&n air filter with no cover. I found a chart which calls for a 170 main, 42 pilot, needle on the second, and the a/f screw 2.5 turns out from seat. Bike does not run properly. Adjusting the a/f screw for two hours now even after reading other forums and I cannot figure it out. It either does not start, starts but shuts off after two minutes of running, starts but shuts off immediately after any throttle is given, or it will stay running and shut off at high rpms. I am doing 1/8 turns if that and I cannot find any sweet spot. Do those jets sound correct. I am also at 1300feet.
 
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