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2006 YZ250F Jetting

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Hi All,

I recently read the Motorcycle USA ride report on the new 2006 YZ250F. In the article they state that Yamaha has changed the needle and is using a 177 Main Jet instead of prior years 182. I have an 04 250F and am using JD's jetting kit and I'm using the red needle and a 188 main (if I remember correctly). My bike runs fine; bottom to top. Would anyone have an idea as to why they went leaner on the main? Could it be the new exhaust. I'm of the understanding the engine basically remains unchanged. Any thoughts? I plan on getting a new 06 in the next few weeks.

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I'm no expert, but maybe different cylinder pressures, scavenging and ports? My 05 has had nothing but mysterious jetting woes, from lean to rich and just plain nasty when it rains. I don't know which where to go, it sometimes runs like a dream with no changes at all.. :banghead:

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A 188 main jet sounds really rich for your 04 YZF (even with a JD kit), unless you are doing a lot of special things. I bet you'd get more power out of the top end if you'd try a main jet in the 180 range. It's a simple change out, and definitely worth a quick test.

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