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Valve Shims or Top-end Rebuild?

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I'm having a ton of trouble kick starting my 2006 crf250r. I recently cleaned my carb out so I don't think that's the problem. Most of what I'm reading says it's probably my valves and that I need to check the clearances. I have yet to do that. I read on another post that if the valve shims are out of spec then replacing them will probably be only a temporary fix and that a top end rebuild is on it's way. Is this true? if I find my valves are out of spec would it really just be better to go ahead and do a top end rebuild? I'm definitely a noob when it comes to engine work but I'm trying to learn and hopefully save a little money by not having to take it to a shop. So if I sound like I have no idea what I'm talking about that's because I don't. Any advice/help is appreciated. Thanks

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If i were you i'd take off your gas tank, then your valve cover them look up the valve shim specs for intake and exhaust valves and if its too tight then it holds your valves open and open them sooner letting air out.

When it would be the top end, any visible smoke? any burning oil?

When it would be the valves, lots of back firing on decel, hard starting

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Well... reshimming can usually be done one time safely. Then keep an eye on clearance changes and if they move quickly, then a top end is needed. Sometimes, they stay put for a long time. But the second time they close up, is time to stop riding and start wrenching. I personally, when I find valves closing up, reshim and schedule a top end in the very near future, I do not wait until they close up the second time.

Typical signs of valves that need reshimming is sudden hard starting when cold but fine when hot.

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As stated above he is right, another thing to take into consideration is be up to date on oil and make sure you do not overheat it. If you overheat your head it can cause the valves to close. and keeping up on oil keeps them cool also. I had a 450 that i adjusted the valves once and rode a full season and never touched them

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