yz426 has very little compression

2 replies to this topic
  • copeking

Posted February 22, 2016 - 05:57 PM


I can kick it over all the way no problem very fast, shimed valves and checked valve seats, with the calve cover off and cams removed i slowely kicked it through the compression cycle and hear it in the timing case, however it brand new wiesco piston and rings also has brand new topend kit and jug is clean, what in the &%$#@! clould this be it blows my mind havent got the bike to run yet what should i do put it back togther and run it with this superlow compression or whats going on?

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • 0bigsilver6

Posted February 26, 2016 - 08:34 PM


Since no one else has replied I will take a stab at this. I read on some other thread that if you kick it over without oil in it, it will act like it has no compression. But if you put the oil in and kick it a few times to let the pressure build up that the compression will get back to normal. So since you just changed the piston, have you refilled the oil? I could be way off on that though.

Did you add an auto decompression cam?

Is the decompression lever jammed? Cable adjusted properly?

  • damnbiker94

Posted February 27, 2016 - 01:21 PM


Could be several issues, but i would first confirm that the valve timing is right.

Related Content


Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

Need help by Goforaride

Dirt Bike   Dirt Bike Technical Forums   Suspension
  • Hot  68 replies

yz250x vs 450 4t comparisons (preferably desert riding) needed by JakeNorthrupYZ450F

Dirt Bike   Make / Model Specific   Yamaha   Yamaha 2-Stroke
  • 9 replies

Is the 2016 GYTR Yamaha YZ450F too fast? by Fryboy

Dirt Bike   Special Interest Forums   Pro Racing
  • * - - - -
  • Hot  241 replies

Join Our Community!

Even if you don't want to post, registered members get access to tools that make finding & following the good stuff easier.

If you enjoyed reading about "" here in the ThumperTalk archive, you'll LOVE our community. Come join ThumperTalk today!

The views and opinions expressed on this page are strictly those of the author, and have not been reviewed or approved by ThumperTalk.