I have been troubleshooting a problem with poor performance for about 1.5 years. What I mean by poor performance is that I can’t lean on the throttle to hard. If I do, the bike actually starts slowing down. Like it it is starved for petrol/air. I have replaced “O” rings on the throttle body, the intake stub, exhaust header gasket, O2 sensor. All the parts I replaced helped just “a little” bit.
What I found along the way was that I had a broken wire to the air intake temp sensor and repaired that and the performance issue was less of a problem to much greater extent that all of the other parts I had replaced before. The bike was still not performing as expected.
I was considering replacing the “coils” and The Daily Rider suggested that I replace the air intake temp sensor. I had already ordered it. What I had noticed while riding, was that when the outside air temp was higher, 70 F, my bike got even more cranky. So I made a guess that the sensor was not reporting correct information to the ECU. What a difference in performance after replacing the sensor! My MPG jumped from 51 MPG to 59 MPG and that was on a nasty windy day! Over all performance is up. Still can’t lean on the throttle to hard, butt, the bike is almost performing normally.
Side note on mileage: In SE Wisconsin we are stuck with reformulated fuel that results in a 20% mileage penalty.
I have ordered the cylinder head temp sensor to see if that will complete the solving of this performance issue. I have to drain the coolant. Replacement of the coolant is due. You will need a 22 MM deep well socket to pull this. You will not be able to fit a wrench on it. Got this replaced today 5/8/2010. Didn't seem to make to much difference.
Replacing the air intake temperature sensor is easy. In the manual that I expect that most of us use: Repair Manual F 650 CS dated 06/01. Remove the side panels as directed on pages 46.5-46-6 , Then remove the air intake box. Then, on Page 13.7, you will see how to remove the Temp Sensor. While pushing in the on the locking clip as indicated, pull the sensor out. There is an O ring to prevent air passing by where it is not supposed to. Use a pair of pliers to grab hold the temp sensor and wiggle it out while pressing the locking lever release.
You do get a O ring with the new sensor. Reverse order to assemble your bike back to the way it was.
Test the operation of your bike before you put on the side panels, just in case the electrical plug is not seated correctly.