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Discussion Starter · #1 ·
Ok so I have a 2006 400ex and it has a problem that I have done so much to try and fix and nothing has worked. When the bikes cold, it starts just fine. When the bikes warm, it starts rough. But that’s not all. When I push the throttle about half way the bike stutters and lags like it’s not getting enough fuel. (Mind that it does only when I’m putting around and half throttle). But the weird thing is that it smokes when I rev it hard like it’s running lean. Almost like it’s running lean and rich at the same time. This all happend after I adjusted the valves. The quad runs amazing at full throttle it’s just when I let off the throttle it starts bogging stuttering and begging for gas. And also after I ride it hard and go to stop it doesn’t idle and shuts off. Like I said it all happend after I adjusted the valves.

Whats done to it carb wise: 175 main jet, 42 pilot jet, needle was raised 1 click, carb was rebuilt which was recent, and that’s about it

It’s got the stock header pipe on it with a hmf slip on, no airbox with a k&n filter, 426 big bore, stage 2 cam.

I need help please let me know ASAP!!!!!
 

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2020 520 rubicon foot shift
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642 Posts
Your needle is too rich, try lowering it a notch.
Being too rich causes the stuttering/skipping and not idling good hot.
Being too lean on the needle will make it hesitate a little bit and lack power, it wont stutter when lean.
 

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Discussion Starter · #4 ·
Ok. I put the needle pin on the second highest slot and it made the quad run amazing. No stuttering, same amount of power, no hesitation. Again my setup is 175 main jet, 42 pilot, air box delete, hmf slip on, k&n air filter 426 bore, stage 2 cam. The kinda riding I do is mx and field riding. I am about 420ft above sea level. Thanks again I had adjusted my needle 3 times and rejeted this thing so many times. Super happy with the result. Thank you Eric.
 

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2020 520 rubicon foot shift
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I went through this years ago building a 440ex.
I had stock jets except for the main, it sounds weird but the big bores suck more gas through the jets so you end up leaner than a stock bore motor with the same bolt ons.
Glad I could help.
 
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