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backfiring on decel

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what does this mean, when I let off the throttle my 02 520sx backfires, is this too lean? is this a jet or the fuel screw?

thanks

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Too Lean. You need a JD Jet kit. For the time being you can improve it a bit by raising the needle all the way and set fuel mixture screw at 2 3/4 turns out.

Dwight

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I just got this bike Saturday, it has the JD kit, I live at 4000ft in altitude. It bogs real bad to when the RPM is low and I turn the throttle more than half way open. Which jet do I need to change.

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Agree with Dwight that stock jetting is too lean but poping is only part related. It means;

1: Exhaust pipe is hot, (normal, but richer idle mixture could cool it down)

2: Outside air is leaking in at the head pipe junction with the cylinder head!

Poping or not you need a needle in the carb that has more taper, JD kit is the simplest way I know. Regardless of the jetting being corrected you need to seal up the head pipe. remove the pipe clean the parts of any oil, then seal the head pipe with hi temp silicone (auto parts store) and let it cure for a few days before you start the bike!

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And yes, you now have a $7500 bike with goop on the exhaust, but don't freak out, so do the rest of us.

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when you say head pipe do you mean the intake or the exhaust?

Exhaust.

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I just got this bike Saturday, it has the JD kit, I live at 4000ft in altitude. It bogs real bad to when the RPM is low and I turn the throttle more than half way open. Which jet do I need to change.

That is not jetting, that is the accelerator pump. Just go over to KTMtalk.com, select the Jetting section, at the top of the page select the pinned article AC pump 101

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