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99 YZF 400 Rich or Lean??

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I'm new to TT and to 4 stroke motox. I just purchased a 99 YZF 400 that was already set up with a White Bros E Series pipe with 12 plates. Due to the noise restrictions at parks I ride I removed 6 plates and installed a White Bros quiet core silencer. White Bros said that this would not require any rejetting or retuning of any sort.

My question is about how to tell if the bike is running rich or lean. Overall, the bike runs awesome and doesn't get hot. However, when doing mountain trail riding primarily in 1st and 2nd gear I notice some popping on the pipe if I'm headed down hill and using the engine as a brake.

I've heard popping on deceleration is an indicator that you are too lean. How about when using the engine as a brake on long downhill slopes.

Thanks,

Steve

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You need not worry about a little popping on deceleration. Yes, it may be slightly lean, but if the bike is running good then you're probably at a safe setting. The '99YZ had a relatively lean needle in the carburetor. You could turn the fuel screw outwards slightly and compare. Keep track of any changes so you can always return to the current setting.

James

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