Knocking in upper.

9 replies to this topic
  • JEdwardsJr

Posted April 10, 2016 - 07:28 PM


Just rebuilt the upper on my 2004 yz450f. Hot cams and high compression piston. After a light riding me and a buddy decided the crab should probably be checked and the shims. We rebuilt the carb today and checked the shims. All set to go. Start it up and it's idling and running smoother but there's a knock in the top end... It got quieter as it warmed up but it's still there. An ideas?????

  • bikedude987

Posted April 11, 2016 - 07:00 AM


Checked, or ADJUSTED, shims?  


If it was fine before and all you did was check things, either you didn't notice it before, or you changed something.  


Did you adjust jetting?  ---> detonation?


Did you unseal the intake tract anywhere ---> air leak?


Did you adjust the valves?  ----> happy valve is a tappy valve?


Need more info...

  • grayracer513

Posted April 11, 2016 - 08:47 AM


If you replaced the piston, what brand did you use?

  • JEdwardsJr

Posted April 11, 2016 - 11:32 AM


Vertex. Standard bore high compression piston. The sleeve was fine and did not have to be bored. The shims all needed .10 more on the intake side. So went from a .175 to a .185 on two valves and .165 to a .175 on the last one. The jetting is all brand new and back to stock setting right now.

  • jaguar57

Posted April 15, 2016 - 10:54 AM


are you using high octane gasoline?

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  • grayracer513

Posted April 15, 2016 - 11:20 AM


Should not need more than 91 octane pump gas, even with 13.7:1

  • JEdwardsJr

Posted April 15, 2016 - 04:21 PM


Checking the timing this Sunday and rechecking EVERYTHING again since us in Colorado are getting snow again. It's a garage weekend so I have time. I am running 91

  • JEdwardsJr

Posted April 19, 2016 - 07:12 PM


Timing is dead on! We have spark and fuel, I can feel compression when I kick it but the bike will not start now. WTF. Lol this thing is becoming a headache.

  • JEdwardsJr

Posted April 19, 2016 - 07:17 PM


Nevermind... Air screw was all the way in....

  • grayracer513

Posted April 19, 2016 - 08:04 PM


That's a fuel screw.  In is lean, out is rich.

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