ASK THE MXPERTS: WHAT DO THE NUMBERS ON A YZ250 NEEDLE ACTUALLY MEAN?

YZ250 NEEDLES & NUMBERS

Dear MXperts,

I know that MXA recommends that I switch the needle on my totally rebuilt 2007 Yamaha YZ250 from an N3EJ to an N3EW, but I’m interested in what those letters and numbers on the needle actually refer to.

A needle functions based on its diameter, length and taper. In N3EW, the “N” refers to the taper angle, the “3E” represents the point on the needle that the tapered section begins, and the “W” is the diameter of the straight portion of the needle. Changing the diameter of the straight portion adjusts the fuel mixture from 1/8 to 1/4 throttle openings (the larger the needle diameter, the leaner the mixture). In 2007, Yamaha took the well-tested advice of local racers and dropped the stock NE3J needle for the N3EW needle. The NE3J needle had a larger diameter and thus was leaner than the smaller diameter of the N3EW.

For tuning purposes, Yamaha offers needles that are one-half clip leaner and richer than the stock 2007’s NE3W (they don’t offer full-clip leaner or richer needles because you could achieve that by moving the clip on the stock needle). The N3CW is a half clip leaner and the N8RW is a half clip richer.

 

 

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