350x backfires horribly...

[secluded]

hello, my 350x has a 400ex carb on it and i do not know whats wrong with it, or where to start looking. all it has is a 400ex carb, (138 main, 42 pilot and the needle is up 1 click) cobra pipe, crappy friggen filter with no lid. what should the jetting be about? any thing will help.

[dads]

Sound like over fueling. Jets may be to big. How much over the stock 350 are they?

[hrc200x]

I always thought back firing was from a lean condition or exghaust leeks. Maybe it depends when it backfires, does it do it when you try to get on the throttle or when you let off and downshift? How does it run? If it runs good and the plug is a grey color then its probably an exghaust leek where the head pipe fits into the motor or possibly where the muffler connects to the head pipe.

[Mobular]

Most important clue is where does it backfire from? The carb or exhaust?

[250sx]

have you checked the plug? try putting the airbox lid back on too.

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Originally posted by Mobular
Most important clue is where does it backfire from? The carb or exhaust?

actually on occasion both. when i let of the throttle and down shift is when, the plug looks a good dark color( i know this means rich to most people but i like them darker) 138 is stock 350x carb, but i got the pipe so i moved the needle 1 clip down. i figure is probably a leak in the exhaust?

[Mobular]

So you didn't upjet when you put on an aftermarket pipe? Try a bigger main jet.

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Originally posted by Mobular
So you didn't upjet when you put on an aftermarket pipe? Try a bigger main jet.

maybe you didn't see it, or just dont know what your talking about, i moved the needle up a notch(like going up a couple main sizes)

[Levi]

Secluded,

That's where you're wrong. Adjusting the jet needle is not like going up a couple of main jets.
The needle jet varies the fuel/air mixture up to 3/4 throttle.

The main jet takes over after that, from 3/4 to W.O.T.

[Mobular]

That's right. The needle is not a main jet.


And I do know what I am talking about, but since you seem to know the answers to the question that you have posed, I'll let you work it out yourself....

[secluded]

Originally posted by Mobular
That's right. The needle is not a main jet.


And I do know what I am talking about, but since you seem to know the answers to the question that you have posed, I'll let you work it out yourself....

someone clearly took it the wrong way :booty: ok i made a mistake, i thought moving the needle was like moving 2-3 main jet sizes, guess i must be 1 of the few on here that admits their mistakes?

[Mobular]

I didn't take anything the wrong way. I worked with the info you provided. I cannot help it if you were wrong, mis-informed or whatever.


Say what you mean, otherwise how can you mean what you say?

[250sx]

chill out guys. no need to go to the fight club over a misunderstanding. :nono:

[Mobular]

No problem, I'm done...