2001 400ex sputtering

[weeman69xx303]

i just picked up a 2001 400ex, i know nothing about it. it has a k&n air filter on it and stock pipes. i am not sure if it has been jetted or not for the air filter but it sputters in the low end of the gears. if i dump the clutch and rip through all 5 gears it runs find and even hung with a stock 250r. if i start out slow though it sputters untill mid to high rpms and then it rides fine. it idles fine and doesnt to it when i just rev it, only when in gear. when riding on the roads or racing on flat land i dont really even notice the sputtering but when i to go do a hill climb where the revs drop it starts to sputter real bad or it i am driving slow just sitting in the low end of the gear. im going to take the carb off today and clean the jets out and possibly throw a stock filter back on and go from there. if this doesnt work i will probably just take it to a shop and have it looked at but i dont wanna spend a lot of money if it ends up being something small that i could have done on my own. and ideas?

[mlabarca240]

Read the spark plug. This will tell you a lot. If it is white-ish in color you are running too lean and need to put in a bigger main jet. If it is black with soot the its running too rich and you need a smaller main jet. Since its idling good i wouldnt touch the pilot jet. Start there and post results!

[weeman69xx303]

I cleaned the carb out. It was a little dirty but it didn't fix the problem. I'm also running a 168 main jet so I'm thinkin I should probably go down

[Racerjames]

I know it sounds as$-hol-ish, buuut...
How old is the fuel?
Reminds me of $hitty gas

[weeman69xx303]

Fresh gas and its super

[weeman69xx303]

just got the quad back from the shop....they had to adjust the needle and its 100% better but now it has trouble at idle....i adjusted the idle a little and it made it a little better. could this have to do with the jet being to big? (i now have a stock filter back on it and stock pipe with a 168 main)

[jasonwayne222]

I had the exact same problem after I put in a higher comp piston, its definitly your carb, you will have to get some jets and play with it, adjust your needle up or down, go up to a 42 pilot, the pilots your idle circuit, and play with the a/f mixture screw, it takes time and patients, try one thing at a time, you need to find someone who knows how to tune a carb if your not capable.

[weeman69xx303]

could it be the4 valves?

[honda400ex2003]

Originally posted by weeman69xx303
just got the quad back from the shop....they had to adjust the needle and its 100% better but now it has trouble at idle....i adjusted the idle a little and it made it a little better. could this have to do with the jet being to big? (i now have a stock filter back on it and stock pipe with a 168 main)

if you took off the filter and have the full stock exhaust you will have to go back to stock jetting.

38 pilot, 2.25 turns out on the f/a screw, 3rd needle position(which is now changed to the 2nd from the lifting it to compensate for the huge main jet), and a 148 pilot. you can change the pilot to a 42 and leave the f/a screw alone but i would def suggest going back to stock jetting now that you changed it all around.

you cant change stuff like that and not expect to rejet afterward. steve

[honda400ex2003]

also while you have it apart to get the carb off, adjust the valves so that you wont have to do that for a while again.

http://www.atvriders.com/articles/valveadjustment400ex.html

just for save measure as long as you do it right. then change the oil and clean the air filter and you will be good to go for quite a while. dont forget there are 2 plugs for the oil.

http://www.atvriders.com/articles/oilchange400ex.html

steve

[AtvKid4Eva]

just put the carb back to stock with a 148 main and it should run fine..if the airbox lid is on then i dont see why the previous owner would rejet it unless he was running an aftermarket exhaust before you bought it. So with a 148 and everything back to stock on the carb is should run fine.

[weeman69xx303]

the guy before me had an exhaust and k&n on it thats why he did the jetting like that and i didnt do the work on the carb so im not sure why the shop changed the filter to stock and didnt touch the jetting

[honda400ex2003]

did you get the k&n back? you could put a 150 in there and go to around 3 turns out on the f/a screw and run the filter with the lid on. steve

[weeman69xx303]

nope i didnt get the filter back but im goin to run out this week and get another k&n and check it out and see if it makes a difference

[honda400ex2003]

if anything and you dont wanna rejet, get a filter and take the lid off. that will get you pretty close with the 168. it will be on the rich side still but will run better than it is now thats for. I would def raise the needle back up, i would be willing to bet money that your mid range will be too lean with a filter and the box opened up. I usually suggest around a 155-165 with a filter and lid off combo depending on the exhaust and if it is full or not. steve

[weeman69xx303]

will that make much of a difference? because it runs perfect now when im riding it and smokes every other 400 i ride with, just has some trouble at idle when its cold out

[honda400ex2003]

it wont make much of a difference imo. a 42 pilot would help it out in the cold for sure. most people do that anyway with all of the stock settings. steve

[weeman69xx303]

ok thanks ill check it out this week