Hello, I recently bought a 2003 KLX400. It runs great once it's rolling but at idle, If I crack the throttle quickly it dies every time. If I start off by gently rolling on the gas it will run fine. Only dies if I let off the gas and get on it quickly or starting from an idle. It always starts right back up But,... when it dies at an intersection or riding trails and I crack the throttle,.. unsafe and not fun.
Any help? I have read an old thread similar but his would die and not start back up or just not run well on occasion. Mine always starts and runs great after gently getting it going.

 

Sounds like a case of air and fuel. Here's my experience and understanding so far, someone pipe up if I get it wrong. There are three jets in most modern carbs. One of them is for idle. It runs, so this one is probably fine. There is also a mixture screw, which sets the fuel/air ratio. It runs, so this is probably fine too. One or both of the other jets ("pilot" and "main" if I recall correctly) are probably blocked or dirty. Take the carb apart, clean it well, reassemble. Hopefully this fixes your issue.

Hope this helps.