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Problems with -02 CRF450

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Hey,

I just bought a -02 CRF450. It ran perfectly for the first week or so but now I'm having some serious problems with it. The bike started twitching when you held the throttle in a steady gas while riding. At first it wasn't too bad but it kept getting worse and worse to the point that I couldn't ride it anymore. I changed the sparkplug and it ran as it should for a while but then the same thing happened, gradually. Now the bike cuts so much that I can't ride it. Even when you have no gear and give some gas to it, it just barely raises the rpm and pops much more than usually when you let the gas go. I cleaned the carburetor and next I'm gonna check and clean the electrics. But if this doesn't help, I don't know what I'm supposed to do with this. At a bike shop someone told me that the bike needs a valve check, so maybe I'm gonna let them do that also.

I'm new to four-stroke bikes so I don't really know anything about how the valves work. And my two-stroke bikes have never given me problems like this, so I'm a bit worried about how much time, effort and money this is gonna cost me. If somebody has had problems like this before or might have a clue what's wrong here, please let me know. I'd appreciate it. Thank you.

Mikko

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Valve clearance check would certainly be in order, but you said something that caught my ear. You said it run good for a while after you changed the plug. Was the old plug black and sooty, or tan or white looking? What did the new plug look like after it begin to run poorly?

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Another thing to check would be to make sure your hot start lever is returning all the way. If that is binding or not going all the way in, your bike will run lean and start backfiring. It will act like a bike does when the valves are going bad.

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