06 crf450 rev problems

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#1
Im having a problem revving my crf. when im ride it in the upper rpms it like cuts out. not only that but when i first got it i couldnt hold the front end down for anything now it seems like im underpowered. i dont think it could be valves because i just rebuilt the whole thing new piston,rings and i sent the head to a porting shop. i need help!!! i wonder if its something electical
 

Rich Rohrich

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#2
Verifying the compression, cam timing and valve clearance would be the logical place to start given the work that was performed.
 
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#3
the valve clearance is ok. i did the timing exactly how it says in the manuel. although im not sure how to check the compression but before the topend was replaced i could kick it over with my hand with ease i shouldnt be able to do that. now its way harder to kick. another thing it usaul starts now withing 3 kicks.
 

Rich Rohrich

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#4
crf122 said:
i did the timing exactly how it says in the manuel.
That's what everyone says when they get the timing off on a CRF450. There are non-symmetrical timing marks on the cam sprocket that have a very specific A/B relationship with the timing marks on the crank. It's very easy to get it wrong the first time.

If it's not running right it's worth rechecking the timing and the valve clearance if only to eliminate them as a possibility. The procedure for checking the compression is outlined in the service manual.
 
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#5
ok i will check i just thought that if the timing was off that you wouldnt be able to start it
 

Rich Rohrich

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#6
crf122 said:
ok i will check i just thought that if the timing was off that you wouldnt be able to start it
It will usually start just fine with the timing off a tooth.