back fire, how can i fix it

[ExVillin400]

hello everyone, i have a little problem with my 400ex. a while ago i put a t-4 slip on, on my quad with a k&n with out jetting it. it ran great. just the other day i took the stock jet out and put in a 160main. i ran it down the street, it ran the same, no power gain, no power loss. when i down shifted it would back fire, so i took te air book cover off to see what happend and it still did it. im stumped the only other thing i could think off is to probably get a hotter plug to clear it up. but why would this happen by me putting a bigger jet in? i thought it only back fired when it was running lean. if you guys can help me out, it would be much appreciatted. thanks

[ryanh250ex]

Originally posted by ExVillin400
hello everyone, i have a little problem with my 400ex. a while ago i put a t-4 slip on, on my quad with a k&n with out jetting it. it ran great. just the other day i took the stock jet out and put in a 160main. i ran it down the street, it ran the same, no power gain, no power loss. when i down shifted it would back fire, so i took te air book cover off to see what happend and it still did it. im stumped the only other thing i could think off is to probably get a hotter plug to clear it up. but why would this happen by me putting a bigger jet in? i thought it only back fired when it was running lean. if you guys can help me out, it would be much appreciatted. thanks

hmm... have you tried messing around with anything but the main jet?

i think you are a bit rich on the mj.i'm not sure, but try like a 155 or perhaps something smaller.

try dropping the e-clip position on the jet needle one notch. also, mess around with your air and fuel screws. i think that you should adjust the fuel screw out some, that way more fuel is coming into the motor on deceleration.

i believe you should be problem-free after you try the things i mentioned. i had similiar problems with my quad, and once i dropped the e-clip position and increased the fuel screw slightly, it runs awesome. it still backfires, but that is only from lack of back pressure.

[sparks400]

do not go down ull be still backfiring go to a 170 main, and 3.5 turns out, but make sure ur adjustment screw is seated when u turn it in and then out, if drop the jet ull be leaning it out more, and u dont want to lean a 4 stroke out, leaning is for 2 stroke, if u have open airbox, exhuats and aftermarket filter ur gonna be running, lean with the stokc jet. but i have the same things expect for a hi-flo head pipe, but try that and tell us how it is

[ExVillin400]

i also took the little cup out that was under the main jet, was that a bad move?

[nacs400ex]

why are you messign with things on your quad if you dont even know what they are? Why did you take it out ?

[250x#93]

Sometimes if ya have an exaust leak they will back fire, might be sumthin to check out:cool:

omg..what did you take out...sounds to me like you are screwed....but I would of done the same thing cause I have no idea about jetting or anything??thats why i got a cobra cause you dont have to jet ith one of them :) (no power gains except a little easier to bring up a wheelie in 3rd)

[sparks400]

if u took off the float thats ok if ur gonna change ur main u should now, if its still off