2007 crf250r won't stop backfiring

5 replies to this topic
  • yamaharider367

Posted July 11, 2009 - 08:40 AM


well to start I haven't been on a 250f since 06 but I missed it so much that i picked up a 2007 for cheap. the previous owner ran race fuel in the bike(not sure what octane i think 110) well i ran that true the bike now im back on 93 pump gas and now it backfires like crazy. every time i ride and let off the gas its just a bunch of backfire. how can i make it stop. bike still runs great just back fires alot.

  • Nick777

Posted July 11, 2009 - 09:09 AM


jetting, mine did the exact same thing, then i changed the jetting and there is hardly any backfiring, if any at all now.

  • yamaharider367

Posted July 11, 2009 - 02:16 PM


i know this will sound stupid but how do i adjust the jetting. I'm good with tools just never messed with a crab before

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  • yamaharider367

Posted July 11, 2009 - 06:10 PM


come on guys help a brother out

  • ebeck

Posted July 11, 2009 - 06:37 PM


Under the carb under the bowl. You can get to it from the 17mm drain plig with out removing the bowl as well. Follow the arrow labeled Pilot jet.
Posted Image

You un-screw it, like this.
Posted Image

It looks like this:
Posted Image

If it is popping when you decelerate you need a larger pilot. 07 with a stock cam you probably need a 72. The pilot size is etched on the pilot jet.

  • yamaharider367

Posted July 11, 2009 - 07:45 PM


thanks. also what exhaust do u have on your 07?

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