2000 Yz426f

My friend just recently bought a 2000 YZ426F today. When he got home and took the bike for a ride he noticed the bike backfiring. The bike doesn't really backfire when being revved in neutral once it's warmed up. The only time it backfires is if you cut the throttle while moving in gear, usually after a moderate throttle opening. Me nor him don't know a whole lot about 4-stroke bikes, is this normal or has anyone had past experience with this, any tips or help would be appreciated. Thanks.

Is it a backfire or a popping sound, if it is a popping sound when cutting the throttle that is normal to some extent. But if its excessive adjust the fuel screw and, or change the pilot jet. I would also put a new spark plug in there and make sure it has fresh gas. Also check the jetting on it also. Here is a good link on jetting. http://www.thumperfaq.com/jetting.htm This is a 250f page but theres a lot of good info on it, with jetting and other 4 stroke stuff.

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