Newb question.

I just got a 01 YZ426 today and took it around the block a couple times just to see what the 4 stroke motocross bikes feel like. I notice that when I chop the throttle at high revs the engine braking causes some snaping and popping that sounds like backfiring.

Is this normal or is this an indicator that I need a new spark plug? It does have an FMF slip on but a slock header. This thing is so obnoxiously loud to my neighboors but I love the sound. All I know is that this is one serious machine and I love it!!!!!!!

Sounds like a jetting issue, maybe running lean.

Decel backfire is usually caused by an air leak in the exhaust system, or lean idle mixture. However, it is harmless at a reasonable level, and some of it is normal for big YZF's. Really loud popping, or visible flames coming out the muffler is too much, but a little crackling on decel is fine, and IMO, it's an indication that the idle mix is about right.

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