OK, I had to come back here one more time to see if I could digest this O2 fault scenario that the OP thinks he has discovered. It wasn't until I got to the last paragraph that I realized that his methodology for computing the actual fuel mileage was quite bizarre.
Mr. usasmartindian is basing his figures on how soon the fuel bars on his instrument cluster disappear, which we have all ascertained, after having these Meteors for a while, gives us a totally inaccurate way to tell how much fuel is actually in the tank! Especially when you get to the last bar or two. We have all seen those bars come and go, like a kid playing with a light switch, which I can only assume is because of the sloshing of the fuel in the tank and also the angle of the terrain that you may be travelling over.
The fuel gauge certainly is one of the Meteor's big shortcomings, for those that like to run their tanks down before a refill. Even the low fuel light plays up, going on and off for dozens of miles after it first appears. Totally unreliable.
The solution to the OP's problem now seems pretty obvious to me. There is nothing wrong with the bike, just his method of computing his fuel consumption.
The proper way to determine fuel mileage would be to fill the tank (only to the splash guard - NOT the brim), record the bike's mileage and then ride until the tank is fairly low again, at which point you note the mileage again and record how much fuel went into the tank to bring it back to the splash guard. Then do the math.
EDIT:
I would add that his estimate of 0.6 gallons per bar is incorrect, for the tank holds, according to the manual,
approximately 15 litres, which equates to 3.99 US gallons, for a bar ratio breakdown of .57 gallons per bar. Of course, the shape of the fuel tank determines how fast those bars disappear as well and there is also the dead stock, unusable in the tank, to be considered.