98 yz400 help!!

5 replies to this topic
  • zebo007

Posted November 15, 2010 - 07:18 AM


Guy's ,

I have a 98 YZ400 I bought from a friend that was scared of the bike and didn't ride it ( He recieved the bike from a trade). He also couldn't start it. Well, after he had it for a while he asked me to see if I can get it started. After a carb rebuild and new fluids the bike was running fine. I kept the bike and rode it for a couple of months while he was trying to sell it. He called me a while back and had me bring the bike back to his house because someone wanted to look at it. The bike didn't sell and it sat for a couple months again.
I pass by his house everyday going to lunch and looking thru the fence I seen the bike Laying on it's side. So, after a coouple of days I called him and asked what he was doing with the bike. He said the dog nocked it over off the porch. when I went over there to pick it up again I tried to kick it over and it didn't have the compression it had before it sat up again. I don't have to use the compression lever any more. So anyway I picked up the bike pretty cheap and need to know what are ya'lls thoughts on what could have happened when the bike fell over. Remember this bike was running like a bat out of hell a couple months ago and was just sitting there. I checked the compression and it was 120. I know it should be more than that but don't know what it should be. Any thoughts would be apreciated.

Thanks, Jason

  • zebo007

Posted November 19, 2010 - 12:14 PM


Anyone? Could it be a ring sticking? If a valve was stuck would it have any Compression? Could anything have come loose from falling over?

  • myoung

Posted November 19, 2010 - 03:43 PM


I'm assuming it still has the manual decompression, did the lever hit the ground and get stuck open? Maybe the cable is stretched and holding the valve open a little bit? That, or he was running it and damaged something. If that's the case he probably threw it on the ground because he was upset. Would explain why he didn't pick it up after 'the dog knocked it over'. Why is he leaving it outside anyway? :p

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  • bluethumper98

Posted November 20, 2010 - 08:50 AM


Definetely check that compression release assembly. I have a 400 to and they are great bikes.

  • nopremix

Posted November 22, 2010 - 10:28 PM


my 400 ended up blowing up a top end when the comp release cable was set too tight.
Yamaha replaced it under warranty, but I learned a lesson to make sure and keep an eye on it. I would zero in on that issue ...

  • 250stroker

Posted December 04, 2010 - 05:04 PM


my dad laid his bike down and it slightly bent the radiator and it was pushing against the decompression lever on the motor. the bike obviosly didnt have the right compression afterward but now the rad is straight...problem was solved!

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