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(How to Resolve or Reduce a Stalling/ Popping Issue Problem)

CO Adjustment

Following is the confirmed procedure recommended by Yamaha to enable the CO adjustment mode on Road and Stratoliners.

The intent of this mod is to permit a proper adjustment in the idle fuel/air ratio, and perhaps a bit beyond, and not violate any emission regulations. This adjustment may allow for a proper idling engine at a variety of altitudes, and may reduce the "popping" experienced by some through slight idle mixture enrichment when the throttle is closed on deceleration. How far above idle this adjustment has an effect is unknown at present, but that probably occurs when the engine goes into closed loop mode and the O2 sensor data begins to take effect. The bike runs in open loop at idle I believe.

The following should duplicate the F/A mixture changes at closed throttle, only previously available by adding an outboard fuel controller. An outboard fuel controller will still be required if F/A ratio changes are desired across the full range of engine RPMs.

The procedure is straightforward and involves adding a grounded wire to the #21 connector position on the largest multi-wire plug that is attached to the ECU. Looking at the larger of the two plugs, it's the fourth hole from the right on the bottom row as viewed from the right side of the motorcycle. There's a Pink with White stripe wire to the left of the #21 plug, and a Solid Brown wire to the right.

To ground that connection, first remove the small white plastic plug inserted in the #21 position. It's a slip fit, and comes out easily with a fine tweezers or prying out with a sharp pin. Save the plug. If desired, after disconnecting the battery, the entire large plug can be removed from the ECU. And after removing the orange cap on the side facing the ECU, the white plug can be pushed out from the plug with a fine pin. That's not required, however.

Next tin with solder about 1/4 inch of #20 insulated stranded wire to keep it from fraying. Fully insert the tinned end into the #21 hole until it bottoms against the Orange cover. That will allow the tinned end to contact the corresponding pin on the ECU. Confirm the complete insertion by noting that's happened by removing the Orange cap on the plug if desired. Crimp and solder a eye to the other end of the inserted wire and install under the battery ground lug next to the oil filler cap. That completes the installation, and the optional wire can be left there permanently if desired, or removed after the CO adjustment and the white plug removed previously reinserted to seal the hole. Reconnect the battery.

Next, follow the directions in the Factory or Online Service Manual for entering the Diagnostic mode. Following is a synopsis of the procedure I used:

1. Turn the main key off (if on), and make sure the red kill switch is in the run position.

2. Press and hold the Reset switch (on the tank on '08's, right handlebar on others), turn on the key switch, and hold until DIAG appears on the LCD screen below the speedometer. Press the Select button (on the left handlebar) to toggle to the CO mode on the screen. If "CO" doesn't show (as in an unmodified bike), then your wire is not properly grounding the #21 connector on the ECU. Inspect and fix as required to get "CO" on the display.

3. When in the CO mode, simultaneously press the Select and Reset switches until C1 appears (about 2 sec.). You're now in the CO mode for cylinder #1 rear. Or if desired, pressing Select will toggle between C1 and C2, the front cylinder #2. Adjust either one as described below one increment at a time until the desired F/A mixture is reached. The best F/A ratio will yield the highest and smoothest idle rpm, but the auto idle system may mask that somewhat. Experiment and return to "0" values if confused.

4. Well, moving right along, press Select and Reset again and a "0" will appear below the CO letters. That's the Factory set relative value for the amount of fuel injected at idle. Press Select to increase that value one unit at a time, or press Reset to decrease the value. Both of mine were Factory set at "0". Values are shown as a -1, 0, 1 for example above and below the base value of "0". The higher the number, the richer the idle mixture, the lower is obvious.

5. When done with the C1 adjustment (or C2), press Select and Reset to save the C1 value you've chosen.

6. Then press Select to choose C2 (or C1), and Select and Reset to enable the "0" value as above. Adjust the value as desired, and close and save the new setting by pressing Select and Reset. Shut down the engine, or go for a ride to test. The added wire can be left installed permanently, or removed and the white plug reinstalled.

All the above can be done while the engine is running, if desired, to note any difference in performance. I plan to go to a local Emission compliance place tomorrow and run the bike stock, and then incrementally adjust the CO to get around 3% idle CO, a value I liked with my FJR1300's. Adding 3-5 units to each cylinder achieved that value on that bike. Also on that bike, anything over 4% (+7-10 units added) was rich and the exhaust smelled sweet like raw fuel. We'll also determine at what RPM the Cat starts cooking the excess fuel with the emission probe. More on all that later.

Enjoy, but please be responsible with your changes.