99 yz400f problems

11 replies to this topic
  • stootypants

Posted July 14, 2011 - 04:28 PM


I have owned a 99 yz400 for a few months now. I accidentally dropped it in a mud hole while riding. I made the mistake of running to get it to my truck to take it home. It ran perfect for several weeks, then... I noticed a rattling in the top end and it didn't want to stay at idle. I discovered there was water in the oil, so i flushed it several times with diesel fuel and oil. The majority of the water is gone, but the problem still exist. Any advice?

  • gscx

Posted July 14, 2011 - 04:40 PM


So you let oil mixed with a lot of water/silt sit in your bike for several weeks and rode it during that time? Only advice I have is to take it apart and see whats wrong. And get a manual if you dont have one.

  • stootypants

Posted July 15, 2011 - 12:08 PM


what is the best manual to get? yamaha, clymer, or something else

  • QuietFlight

Posted July 15, 2011 - 12:54 PM



they have them for free here. search around a bit.

  • stootypants

Posted July 16, 2011 - 05:05 PM


thank you for your advice, but i was trying to get an idea what to check or possible problems to cause these issues. I guess I'll have to get the manual and check everything. I really just wanting to know if its carb related or if its something internal or what.

  • grayracer513

Posted July 16, 2011 - 05:38 PM


You had muddy water in your engine oil. Time to tear the engine down and flush out the tank in the frame.

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  • ttr250dude

Posted July 17, 2011 - 06:53 PM


Change your oil filter too. It's probably full of dirt and whatnot right now. Since the sound is coming from the top end, the first step would be to take off the head cover and go from there.

  • stootypants

Posted July 18, 2011 - 02:28 PM


thank you for the advice, i just got the oil flushed and changed the filter, im gonna clean the carb and see what happens. I'm trying to avoid going in the bottom end. Everything in the top end seems good. Im hoping its just water and or dirt in the carb. Ill keep everyone posted.

  • ttr250dude

Posted July 18, 2011 - 03:40 PM


If theres a rattling in the top end i doubt it's a carb problem.

  • stootypants

Posted July 19, 2011 - 03:11 PM


i tried running it off straight starter fluid and it ran perfect, no noise or anything. Does this mean it's just a carb issue?

  • grayracer513

Posted July 19, 2011 - 06:34 PM


That's usually a good clue, yes.

  • ttr250dude

Posted July 19, 2011 - 06:37 PM


I'm stumped, my guess is carb problem. I'm guessing Gray has useful advice, as usual haha

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