compression test

6 replies to this topic
  • riderman329

Posted February 11, 2005 - 07:23 PM


i did a compression test on my 04' 450f and i got 30 psi is that right? i can't seem to find anything in the owner book about it at all!

  • sanpedro426

Posted February 11, 2005 - 07:41 PM


i think it should be way over 120 psi. I think greyracer would know.

  • riderman329

Posted February 11, 2005 - 07:52 PM


yeah but on auto-decompression motor, your automatily lose the compression on the kick? so what going on! :)

Visit the ThumperTalk Store for the lowest prices on motorcycle / ATV parts and accessories - Guaranteed
  • sanpedro426

Posted February 11, 2005 - 08:25 PM


Yea thats a good point and i dont know the answer. :)

  • grayracer513

Posted February 11, 2005 - 09:50 PM


You can do a compression test, but you have to disable the decomp mechanism to make it meaningful. Remove the cam cover. Insert a piece of card stock such as a matchbook cover under the flyweight on the exhaust cam so that it will hold the weight in the full out position against spring pressure, and so that it will not fall out and escape into the engine. Do your compression test and be sure to remove the wedge when you're done.

  • markyz450

Posted February 13, 2005 - 03:26 PM


most enigines w/ compression releases have specs in the 50 - 100 psi range.
i have an 03 450, i checked mine recently and got ~70 psi. yamaha is the only manufacturer tha does not give a spec for comp. pressure in their service manuals. with comp. release dissabled a would expect a reading more like 175- 200psi.... but 30 seems waaaay low.

  • riderman329

Posted February 13, 2005 - 06:27 PM


i redid the test today and i got 60, i forgot to open the throttle!

Related Content


Yamaha YZ450F 2017 by Chris.GVS

Yamaha YZ450F 2017
  • - - - - -
  • 0 reviews
WR Camshaft Swap Info - last post by jamesm113

WR Camshaft Swap Info

  • 0 replies

Thinking about Yamaha 250... by Arctic Pride

Dirt Bike   Special Interest Forums   Pro Racing
  • Hot  491 replies

Snake pit oct 30th by The Anvil

Dirt Bike   Dirt Bike Regional Discussion   California
  • Hot  293 replies

Michigan Motocross Tires by 288yz450

Dirt Bike   Dirt Bike Regional Discussion   North
  • 1 reply

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.