Rebuilt 08 yzf450 trouble starting?

5 replies to this topic
  • jbeiter93

Posted June 03, 2012 - 06:14 PM


Me and a buddy just rebuilt my 08 yzf450 when we got it all back together it started up with less than 10 kicks and ran fine. We took it out to break in the motor the next day and it started right up on the first kick ran for 10 mins fine but started to bog and then died and we have not been able to start it since. It has low compression. If anyone has an idea of what it might be please help it would be greatly appreciated

  • marv02

Posted June 03, 2012 - 08:46 PM


Is you'r compression release stuck in the open position ??.

What is the compression gauge reading how many pounds is it showing.

Put a little motor oil into the spark pulg hole put the plug back in and see if you get better compression if you do it you'r rings.
Or it could be a gouge in the cylinder wall sorry it happens.

Or put some compresssed air in to the spark plug hole with intake and exhaust valves closed see if it holds the air pressue if you have a valve thats hanging open the air will come out either the intake of the exhaust port.

If bad rings the air will come out the oil fill hole.

Oh ya it could be a bad head gasket.

Edited by marv02, June 03, 2012 - 08:48 PM.

  • grayracer513

Posted June 04, 2012 - 06:57 AM


The compression release cannot stick in the open position, and if it did, the noise would be very noticeable.

Compression gauges are essentially useless because of the auto-decompression system. A leak down test is the only correct diagnostic to use.

Start by checking the cam timing and valve clearance.

If you failed to replace the cam chain, or if you lapped the valves, or failed to follow the correct head torquing procedure (torque, loosen retorque, then rotate 180 degrees) your problems could result from that.

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  • jbeiter93

Posted June 04, 2012 - 07:27 PM


Well its definitely timing it keeps hopping time by a couple teeth so i ordered a new tensioner and am prolly gonna get a new chain as well but im gonna try the tensioner first. I also think we are timing it by the wrong marks on the magneto so now i feel like an idiot haha

  • grayracer513

Posted June 04, 2012 - 08:35 PM


Trust me on this one. The chain is the cause. Replace both. You're almost guaranteed a failure if you don't.

Even if I'm wrong, it'll only cost you another $40 for the chain and a flywheel puller.

  • jbeiter93

Posted June 07, 2012 - 10:00 AM


I already got all the parts on order and ill be putting a new tensioner and chain on thanks for the help guys hopefully that will fix the problem

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