My 06' crf450X won't rev but idles fine

I have an 06' 450x. Out of the blue she won't rev up. She starts great and idles fine. Gas is fine, oil full, air cleaner clean, muffler clear. As soon as I twist the throttle it backfires and dies. ***!

Have you done any work on the bike lately.

New exhaust pipe. I'm changing the plug just so I don't look like a total idiot.

New exhaust pipe. I'm changing the plug just so I don't look like a total idiot.

Have you re-jetted the bike? If not, you made a lean bike even leaner so read the jetting stickies. A symptom of a lean condition is the backfiring sound you mentioned.

Jetting is critical. You may also have some crap that clogged your main jet. Open the carb and re-jet like the guys mentions above or clean it out if its clogged. Your prob is most likely in the carb.

New exhaust pipe. I'm changing the plug just so I don't look like a total idiot.

So, you still have the stock jetting then?

You need to adjust your fuel screw to match the new pipe, if you want it to start, but really you need to re-jet the carb if you want it to run well.

Thousands of posts on this.

New plug and now it won't start....I'm going to take the carb out, rejet it, and clean it up. This is a great site, thanks for the feed back guys.

New plug and now it won't start....I'm going to take the carb out, rejet it, and clean it up. This is a great site, thanks for the feed back guys.

Please don't use automotive carb cleaner; it will damage parts. Use MC cleaner or Brake cleaner.

check ap diaphram

I had similar but not as severe symptoms with my bike (same year even). I re-jetted and adjusted the fuel mixture screw which helped but it still couldn't take a full blast of throttle without killing it. I finally had it worked on and the accelerator pump diaphragm was the culprit.

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