YZ400 lost power

10 replies to this topic

Posted February 27, 2005 - 07:33 PM


I just put a YZ400f motor in my atv about three months ago. Last night at an arenacross it all of the sudden lost power and the engine sounded like it was dragging really bad and the head pipe turned red about six inches from cylinder. I also could here compression coming through the air filter when I was trying to crank it. I'm thinking maybe a valve or two stuck open. Any advice would be appreciated.

  • 02YZ426

Posted February 27, 2005 - 08:23 PM


Does the motor still turn over ok? Does it still run? if it doesnt I would take the head off the engine and have a peek. See whats going on in there, thats really the only way to know whats up.


Posted February 28, 2005 - 05:57 AM


The only way to crank it is to pull it off. It just sounds like it is in a bind, and you can barely hear the exhaust.

  • yamahauler44

Posted February 28, 2005 - 07:28 AM


the head pipe glowing red is normal


Posted February 28, 2005 - 08:43 AM


Yea I know, but not within 30 seconds after getting it running.

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  • sanpedro426

Posted February 28, 2005 - 11:27 AM


Yes it is normal.


Posted February 28, 2005 - 02:05 PM


What about the running sluggish and the compression coming back through the air filter.


Posted March 02, 2005 - 11:20 AM


Somebody must have some ideas.

  • Butta

Posted March 02, 2005 - 12:40 PM


Check the timing. A cam gear could have slipped on the shaft, changing your timing. Sounds like it could be the cause....


Posted March 02, 2005 - 01:28 PM


I'm gonna pull the head off tonight, so I will look at that before I go any farther.


Posted March 03, 2005 - 08:19 AM


Thanks Butta, the intake cam was out of time.

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