It all started one summer, I had a EFI light flashing and a bad coil code pop up but when I started messing with wires the code went away and it seemed to run fine.
Then all of a sudden the next summer my gas mileage dropped from the low 40's to the low 30's. I didn't have a bad coil code so I thought it might be the air filter or plugs. Air filter was fine and changing the plugs had no effect on improving the mileage.
By now I was thinking something was wrong with one of the coils. I removed one of the spark plug wires from the rear cylinder to see if it was sparking. The first one sparked but it seemed weaker then the second one. The second one zapped me good and the first one not so much.
I then reconnected the rear and disconnected the front, at idle I could not tell any difference in how the motor idled when I removed the wires. It always sounded the same.
At this point I figured everything seems to work but my gas mileage is still sh#t. Well, way back when the code first popped up I bought a new coil (Aprilia) and threw it in my tank bag incase the EFI ever started flashing again. Even though all the coils seemed to be sparking I figured throw the new coil on one plug at a time and see what happens.
As you may have guessed by now I picked the coil that didn't zap me that bad as the first test dummy. Well low and behold the gas mileage was back up to the low 40's, and it's stayed there for the last 5 tanks of gas.
I can't say this will work for everyone but I put up with low MPG for a year and I am happy I could figuare this out on my own. If this didn't work I was going to have to take it to the shop because I new the reserve light shouldn't be coming on when the trip meter hit 140's.
The bike has 36,000 miles on it and it's a 2004.