Jetting help?

2 replies to this topic
  • torrmentor

Posted November 06, 2007 - 03:21 AM


Coming into the last few weeks here in NY where the weather is finally cooling off and becoming seasonal(50-60's F, sea level), my bike seems weaker in roll-on, and through the low end (as accelerating out of turns). Although the bike was hard to start while riding last Wens, I think this was due to the bike getting flooded a bit because the throttle got twisted inadvertantly while on the stand. When I pulled the plug, it was black and sooty(sp?). The bike is an '05 YZ 450 with 30 hours on it. What jetting are you guys trying this time of year? I'm just confused, even with my thread searches.
The bike seemed to be bogging last Saturday, could be jetting related, but then I found a clogged vent tube also.:worthy:

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  • jbrooks26

Posted November 06, 2007 - 05:46 AM


Generally, when the temps drop the air gets more dense. This can cause a lean condition, usually corrected with the fuel screw adjustment. If you get more than 2.5 turns out then you will want to try a larger pilot jet and start with your fuel screw back at 1 turn out and make adjustments from there. However, if your plug was not clean then that could be the whole problem right there. I would start with a new plug and go from there. If you are not sure about the jetting then just note the current position of the fuel screw and start playing with it. Turn it in and out at 1/4 turn per adjustment and see where it takes you. More than 2.5 turns out, larger pilot jet, less than 1 turn out, smaller pilot jet. Hope this helps.


  • grayracer513

Posted November 06, 2007 - 07:00 AM


You can figure one larger main jet size (i.e. 165-168) for each 15 degree drop in temperature and be fairly accurate. Pilots are a little less touchy; more like one size for each 20 or so. "Results may Vary"

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