YZ400F Won't Start

3 replies to this topic
  • Peter S.

Posted April 03, 2015 - 11:29 PM


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. 

  • springer8828

Posted April 04, 2015 - 05:57 AM


As funny as this may sound check your spark plug

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  • grayracer513

Posted April 04, 2015 - 06:10 PM


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.

  • Peter S.

Posted April 07, 2015 - 10:25 AM


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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