I Dropped
I carefully check my mileage at every fill-up, and 90% of the time buy my gas at the same pump at the same station, pointing the bike the same way to ensure accuraccy. My first four tanks were all in the 70's, then I had something like a 68, and then more 70's. When I went to the same dealer as Bill, my mileage instantly dropped to the mid-50's, and while with extreme care and babying I managed to get back up into the low 60's, I've not seen 70 again since.
I took it back, and the dealer basically not only told me I was wrong about the backfiring and chided me for complaining about a "remarkable" mid-fifties per gallon, but tried to charge me for the experience (in three digits) after explaining that the warranty would not cover me unless something was actually wrong. Which clearly, he said, was not the case.
My machine backfired for a while after this first service, usually lightly but sometimes quite noticeably. Eventually I suffered one collossal mother-of-all backfires so intense that it felt like Hank Aaron had slammed the bottom of my bike with a Louisville Slugger. (Indeed, I stopped to see if I had hit something, but I found no evidence of this, and the road was completely clear of debris when I went back and checked.) Since then, the backfiring has practically vanished, and my mileage has climbed back up into the mid-60's for the most part. Still, though, given the way I ride I should be breaking 70, like I used to. Nothing has changed save the tuneup.
I probably never will break 70 again, either, becasue recently I installed a Givi E-52 top box. I've no data on this yet, but I hear they cause noticeable drag. <sigh>.
