03 YZ450F carb issue

2 replies to this topic
  • Frankenhonda

Posted February 05, 2010 - 11:39 AM


I just bought a 03 YZ450F, the bike hesitates and stubles when throttle is just barely open/holding it steady while cruizing. If I twist it more it takes of fine, and if Im on it hard its fine, it just when the throttle is holding steady that it has problems..

Any ideas on where to start??

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  • grayracer513

Posted February 05, 2010 - 02:24 PM


Check the pilot screw setting:

Then check the condition of the vacuum release plate on the back of the slide. Be sure it's in right side up ("square side", with the hole near the edge, goes down), and that it's not cracked or missing a corner.

Then check the needle position. Should be near the center. If it's higher than the 5th spot (counting down from the top) try lowering it by moving the clip up to the 4th groove. If it's lower than the 3rd spot, do the opposite.

If all that checks out, disconnect the TPS and try it.

Consider too that it may be that the carb just needs cleaning.

  • Frankenhonda

Posted February 17, 2010 - 12:46 PM


Checked the vacuum release plate it and the seal looked to be in good shape.
Needle in the 4th position

Blew out all the jets Found I have a 170 main and all the other jets are stock but i also found where a piece of the carb has been broken where the pilot jet goes??:ride:

Posted Image

Put a 38 Pilot in and it will still runs with the pilot screw turned all the way in and the hesitation seems to be better with this set up then any other but is still there. It has a Zip-Ty racing fuel screw, Im guessing this broken piece on the carb is affecting it or the fuel screw is not really working as well as it should.

Edited by Frankenhonda, February 18, 2010 - 08:05 AM.

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