Popping when revved and fast idle

Recently my bike began fast idling cold/or hot and when revved popping on deceleration. The jetting hasn't been recently changed, there has not been a recent change in whether and the bike has been setup how it is for as long as I've had it. The only thing I can think of is off and on I've used VP U4 and maybe the jets are not true because of gumming. I haven't taken the carb apart but before I do I was looking for a little feedback from the bluecrew to assist. Thanks in advance :D My bike is a 98 yz420, ported head and full pc ex. system.

Sounds like you have an air leak, check the boot between carb and head and the exhaust seals. Also see that you haven't dropped your fuel screw, the one under your carb.

^^^^^ Sound like good advice :D ^^^^^ Start there and if that doesnt work I would take the carb off and give it a good cleaning.

the popping is due to being to lean, richen up your air/fuel screw and it should go away also the fast idling when revved is another sign of being to lean. :D

the popping is due to being to lean, richen up your air/fuel screw and it should go away also the fast idling when revved is another sign of being to lean. :D

This is true but since he says nothing has changed in the setup recently, that leads me to think its more likley an air leak causing a lean condition. It could be the carb settings too but I would check for air leaks first before messin with the carb.

I'm going to take the bike out tomorrow and run it after making some changes and see what happends. Thanks for the advice guys and I'll post results tomorrow.

U4 will gum up the carb - it must be drained after each use...... but it sure makes power :D

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