YZ 400F Loss of compression

4 replies to this topic
  • blu400f

Posted July 20, 2006 - 10:20 AM


I just got done cleaning the carb, replacing the throttle cable and changing the plug on my 99 YZ 400F. After I got it all back together and went to fire it up I had a huge loss of compression, it will kick all the way through with little resistance like a 125. Before I could not get it to turn all the way through without using the compression release, the plug is tight and the compression release is not stuck open. Anyone else have any idea of what it could be???

  • huffster

Posted July 20, 2006 - 12:18 PM


Was it running before doing the carb clean ?? Sounds like you might have jumped time or have bent a valve....Why did you decide to clean the carb ?

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  • Zique

Posted July 20, 2006 - 12:26 PM


Try to bump start the bike to get it running again. Ride for a sec and then shut it off and see if you have compression again. After doing the BK mod on my bike the same thing happened. I bump started and it has been normal since.

  • blu400f

Posted July 20, 2006 - 02:20 PM


I just thought I would give it a good cleaning while I was replacing the throttle cable. I have owned it for a year now and never done it. It ran fine before. I will try bump starting it tomarrow and see what happends

  • blu400f

Posted July 21, 2006 - 09:13 AM


I got the bike running and its all back to normal, Thanks!!!

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