2003 yz 450 f runs rough at a constant speed

5 replies to this topic
  • motolawson

Posted September 07, 2004 - 09:01 PM


bike runs rough at a steady pace but is smooth and strong upon acceleration????

  • fershy

Posted September 07, 2004 - 09:30 PM


rich on the needle! lean it a clip position and see if that doesn't clear it up.

  • jdd123

Posted September 08, 2004 - 07:38 AM


My 04 did it at 1/4 throttle 1st or 2nd gear. Had a hard time proving it to the Yamaha mechanics. If you cannot correct the problem by jetting, then try the Vortex CDI. It has several settings that eliminated the problem for me. It also depends on how you ride. As I am getting comfortable on the bike, I do not notice it on the MX tracks as I am either accelerating or letting up on the gas. However, out in the open or trails, I use consistant throttle so I have to select a Vortex CDI setting that does not have the stutter. Vortex said that the stutter is a result of the CDI interpolating between maps based on throttle position. While it is interpolating, it drops the voltage to the spark plug way to low.

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  • del_scorcho

Posted September 08, 2004 - 12:28 PM


I had that same problem but didn't know what it was. I very rarely ride at a constant speed so I didn't bother to investigate. CDI huh? Good to know.

  • tool

Posted September 09, 2004 - 02:04 AM


rich on the needle! lean it a clip position and see if that doesn't clear it up.

i had the same problem, i leaned my needle one clip and now its totally gone. :thumbsup:

  • ovrrdrive

Posted September 09, 2004 - 02:34 AM


Mine does this too... But I remember seeing a bunch of posts a while back saying it was normal for this type of carb on a race bike.

I'll try the needle when I get a chance. I did richen the needle up a few months ago...

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