Here's how to remove the factory plug over the idle mixture screw on a 2008 Yamaha XT250 carburetor without removing it from the bike:

1. First loosen the choke lever with a 17mm wrench and move it aside.
2. You will need a 3/32" high speed speed drill bit and a bit extender at least 5" in length or just a long 3/32" drill bit. Drill a hole in the plug, being careful not to drill into the mixture screw behind it.
3. Drive a screw that is slightly larger than the drilled hole and long enough to grab it with pliers. Gently wiggle while you pull to remove the plug.
4. Be careful when putting the choke back on that you do not over tighten the plastic nut.
5. Now you can use a #5 standard or flat blade screwdriver to set the idle mixture screw.

With the exhaust system uncorked, my XT runs best with the idle mixture screw at 2-1/2 turns out, which is exactly what Yamaha recommends. However, after removing the factory plug, I found the idle mixture screw set at 2 turns out from seated. This my have helped with emissions but caused a poor throttle response and a longer warmup time.

Credits: Yamaha related tech tip by Ms. Lil' Mynx. Edited and published by 4Strokes.com.

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