YZ400F Won't Start

Hey all,


I have a 1999 yz400f that I took on a series of desert rides over the last week. All week the bike ran perfect, started in 1-3 kicks, and was a genuinely joyous bike to ride. Coolant always topped off, ran on non-ethanol 92 gasoline. Oil changed every 12 hrs. On the  last day of riding, I started the bike first kick when I unloaded it. It ran for around 10-20 seconds before I hit the kill switch. around 5 minutes later, I started it first kick again to warm it up. It ran for 5 seconds then died. It has not started since. Fuel was on, air filter clean, and I have tried kicking and bump-starting repeatedly. I have tried choke and hot start on, off and every combination of the two. Nothing. It will not start. Why is this? I suspect a fowled plug, although I have never had a 4-stroke do this before.  Bike makes good compression. Any thoughts? Thanks in advance. 

As funny as this may sound check your spark plug

With the older YZF models, the 400's and 426's that have a frame mounted coil and a plug wire, always start with a fresh plug.  The ignition isn't very strong at cranking RPM, so it doesn't take much to foul them.  It's wise to check to see if you have spark, of course.

Replaced the spark plug, Bike started second kick, smoked like crazy for 3 minutes, then ran exactly normal. Carb also overflowed gas for a few minutes, then functioned normally. Old plug was black and the gap was smaller due to the end being bent in.

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