2012 Yamaha YZ450F idles for 10 to 20 sec's siezes up then free's up?

2 replies to this topic
  • MUSHU88

Posted August 18, 2015 - 08:58 AM


Hey Guys 


MUSHU here real name William ive got a small maybe big problem on my baby.. went for a ride with my friend's with no problem at all after about 20 minutes of mixed ridding my bike gave a quick bog then after about 2 minutes just died at idling.. kickstarter was hard and would not budge but after about 2 minutes of waiting it freed up with no problem.


started her up again, idled for 10 to 20 seconds then died again siezed up.. waited then ok to start again.. 


ive pulled the cams and checked if all is in spec all that is ok.. mech alredy polished cam caps due to a little bit of wear but minnimal polished right out now im clueless dont know what to do next or where to check 


any suggestions on what could cause this?

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  • grayracer513

Posted August 18, 2015 - 09:49 AM


Is the kick crank actually frozen, or could it be that you're feeling extremely high compression?  In certain situations, the engine can be stalled against the start of the full compression stroke so quickly that the decompression pin becomes trapped against the valve lifter, and does not have time to extend into an operative position before the engine stops.  In that6 case, you should be able to put the bike in gear and pull it backward off of compression, which will allow the pin to extend and restore normal starting. 


If the engine is actually seizing, the most likely culprit is a badly worn rod bearing.  The rollers can skew off line and jam the rod on the crank.  Fiddling around with it unjams them and it runs again.  It could be cams seizing, but that would most likely result in jumping time if that were the problem.

  • MUSHU88

Posted August 18, 2015 - 10:34 AM


grayracer513 it jams up the motor some how put if i put it in 4th gear and push it backwards then it moves but goin forward again just holds it. opened the cam cover a while ago and saw that it stops right when the intake lobes start to compress on the valve caps. 

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