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Hey I need help. I just replaced Intake valves on My sons 04 crf 250r.I got them from rockeymountainatvmc.They are the prox stainless steel valves and spring kit.I replaced because I was constantly haveing starting issues.After inspecting old ones the old left valve was cupped. So my question now is should I have to go back in and reshim.Since changing he has riden about 25 hrs,and bike is back to having a hard time starting. Thanks for any help

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You had the valve seats re-cut or replaced too didn't you?  If not, that could very well be your problem.  At a minimum, they should have been re-cut.  Even better, replace the OEM seats with copper beryllium.

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New valves means re-cutting the seats, springs to match, and while you are in there, change the timing chain and adjuster. 

If you are on your 2nd piston, you should consider changing the valve guides too.

 

All this work requires profeesional tools and experience.

 

I'd send it out.

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You should never replace the valves without having the seats cut by a reputable machine shop that uses a Serdi or comparable machine and checks to make sure concentricity is within spec. Not doing so is going to be a complete waste of money spent on new valves. I also agree that you should replace the valve springs the same time. They are cheap. With a fast pro racing one of these they should be able to get close to 50 hours on the valves. If its a beginner junior that doesnt bounce of the rev limiter they should be able to get even more hours on it. 25 hours is a very short life for a new set of valves and you are risking breaking a valve as concentricity is probably not within spec.

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