07 YZ450F runs rough off bottom

5 replies to this topic
  • DesertRacer2

Posted March 13, 2012 - 03:06 PM


My 2007 YZ450F has started running rough off the bottom. Mid range to the top end is normal and strong as ever. I checked the pilot and main jet, everything is clean. Valves are in spec and my air filter is clean. Fuel flows strongly out of the tank and I also installed a new spark plug. Am I forgetting something??? Thanks.

  • grayracer513

Posted March 14, 2012 - 08:42 AM



  • DBOBYZ450

Posted March 14, 2012 - 11:45 AM


is it "rough" or just seems like it is at a loss of power. my 07 was losing power, and bogged out when i snapped the throttle in neutral. my timing was bad, i had skiped teeth. my shop thought it was jetting as did i.

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  • DesertRacer2

Posted March 14, 2012 - 08:54 PM


It runs like the pilot jet is clogged but it isn't. It runs fine in the mid range through the top, but the bottom feels like its not getting enough gas. Kind of misses and back fires. The next thing I was going to check was the needle jet.

  • grayracer513

Posted March 15, 2012 - 06:22 AM


See this post: http://www.thumperta...726#post8021726

It's very common for a pilot jet to have a film of varnish deposited in it so that while it may appear clear, its effective size may be reduce very significantly. It only takes about .001-2" to turn a #45 into a #35. You'll want to be sure that the passage that runs past the pilot fuel trim screw is clear, and that both orifices are open where they enter the air stream under the slide. Also be sure that your hot start is closing.

  • DesertRacer2

Posted March 15, 2012 - 03:07 PM


Sounds good, thank you!

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