The initial writeup for this is in the YZ450 thread. I have translated the directions to be specific to the WR450 Thanks to Navaho6 for the initial write-up of how to use the Yamaha FI diagnostic tool to reset CO levels. I just received my tool and reset the CO level, very easy once you fabricate a blade terminal for the green wire. My write-up is specific to 2012+ WR450F. Thanks to WRF-Rowdy for his clarifications on tool use. Yamaha FI Diagnostic Tool - WR450F Directions for resetting CO level Have the ignition key and power button turned OFF! Page 9-26 Yamaha  Owners' Service Manual WR450FB: Remove the seat, open the air filter cover. Disconnect the coupler for the connecting optional part [poor translation from Japanese] Hook the alligator clamps from the diagnostic tool to the bike's battery. Display on tool will read "connecting" but it is not really connecting. You must complete step 4 below before the tool will do anything. Do not press any buttons until you get to step 4. Insert the blade terminal [that you have fabricated and that is attached to the green wire of the diagnostic tool] into the middle terminal of the coupler for the connecting optional part. Here is a link to a picture of the "coupler for the connecting optional part" on ThumperTalk taken by WRF-Rowdy [yellow ellipse] http://www.thumperta...ttach_id=239242 While holding the "Mode" button down on the tool, turn on the bike's key and press the ignition button to power up, then release the "Mode" button. The word "Diag" now shows on tool's display. Press the up button. "CO" shows up on tool's display Press the "Mode" button . "C1" shows on display. Press "Mode" button again. "C1" shows up with a "0" next to it. Now you are ready to set the CO Level. Pressed the up button and display of "0" increases to "1", to set a negative CO reading press the down button. Continued pressing the up or down button until you get the desired CO setting. The new CO level is now set. Apparently a negative CO setting results in better starting [stock setting of zero and positive settings are too rich, especially at altitude], for example, go with -8 initially. Disconnect alligator clamps from battery. Disconnect tool from the "coupler for the connecting optional part" Reinsert the coupler for the connecting optional part back into its receptacle. Close the air filter cover and reinstall the seat. You can now start your bike. Ride the bike and test it. Reset CO level if required to improve starting. If this description need corrections let me know.