03 YZ450F Starting problems

10 replies to this topic
  • BigBearzFan

Posted July 06, 2008 - 04:31 PM


OK here's the deal, I have an 03 YZ450 that is about to drive me nuts. I put a new timing chain on it the other day, put it together, kicked it 3 times fired up and ran fine. Took it to the track today kicked my butt off and it finally started and ran great. Shut it off, took a break, 3 of took turns kicking and it wouldn't start. Went back about 45 minutes later, started 1st kick ran great. Shut it off, to take a braek. Hasn't started since. I 'am tired and my leg is sore from kicking. PLEASE help.

  • Dirtbiker05

Posted July 07, 2008 - 04:36 AM


i would double check to make sure that the valves are in spec then go from there.

  • Ga426owner

Posted July 07, 2008 - 06:43 AM


Did you set the timing correctly?
what about a valve adjustment?

  • BigBearzFan

Posted July 07, 2008 - 09:20 AM


Timing is dead on, Pretty sure the valves are to

  • Ga426owner

Posted July 07, 2008 - 09:43 AM


Then it is either a fuel issue (CArb)or a CDI failure or simply a sparkplug

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  • SUnruh

Posted July 07, 2008 - 09:49 AM


it is possible that the timing chain jumped or the cam gear spun on the shaft.

make sure the cam lobes are at 2 and 10 with the timing marks lined up.

  • BigBearzFan

Posted July 07, 2008 - 04:33 PM


Changed the plug 1st thing when I started having problems. I don't think its a timing issue because it runs to good when it does start. My thoughts are the pilot jet or CDI beaking down. Does this sound logical??

  • grayracer513

Posted July 07, 2008 - 05:59 PM


Idle mixture is probably off.

Do you position the engine in any certain way in order to start it?

  • mjw1

Posted July 07, 2008 - 06:46 PM


your pilot jet might be plugged or you may need to put the next size in it.

  • BigBearzFan

Posted July 08, 2008 - 08:10 AM


I find TDC then kick

  • grayracer513

Posted July 08, 2008 - 10:15 AM


By find TDC, do you mean you find the "hard spot" of the compression stroke, or push it past that to TDC?

The correct way is to come up against compression, reset the lever for a full kick, and then kicking through from there. Some make the mistake of over-thinking things by attempting to get over TDC to start the kick. When that is done, the force of the starting stroke is pretty much exhausted by the time the next compression stoke comes around.

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