'03 Spirit 750, bought new with 125 miles on it, and now have almost 50k. Have added Cobra drags, Mustang seat, MS Fats windshield, National Cycle clear handguards, Kuryakyn ISO flame grips, diamond-shaped flame mirrors (too small, though) HD flame pegs, Passenger and driver backrests, Billski taillight, changed turn signals front and back, added spotlights, and changed out headlight with VTX model. The first mods I did were to install the grips, mirrors, pegs, and pipes, and changed out the sockets in the rear turns for 1157 socket, and painted the lenses red, so they could be running/turn lights, which worked great. Sold them later, and got some smaller 'bullet' type turns, but they're the 1156 type, and just haven't gotten around to change the sockets out since I'm not sure about 'space' inside them. They're really small, but I like the look, though I want more light on the back. When it came time to change out the chain/sprocket, I went to a 39-tooth, verses the stock 41-tooth, and highway use was much improved, but this last time I changed to a 38-tooth, and it's even better. When I first got the bike, I was shifting into 5th gear at 45 mph, and with the 39-tooth it was about 50-55 mph, but with the 38-tooth, I don't get into 5th gear until 60 mph! Highway speeds are PERFECT, now! Recently, I also got a K&N type chrome spike air cleaner off eBay, and was going to install it when I had the sprocket/chain installed, but I guess I didn't have the right jet kit, which came with the pipes, but shop installed the jet kit I had anyway, and now my gas mileage has dropped tremendously, which I'm NOT happy about. I used to go between 120-130 before hitting reserve, and NOW I'm barely getting over 100! That's a HUGE difference, though the bike seems to have s SLIGHT bit more power, it's not THAT much. When I get the spike air cleaner installed, though, after I get the Stage 3 jet kit for the bike from carbjetkits.com, I'm hoping the gas mileage won't drop again by another drastic amount.
As far as 'troubles' go, the main thing that I've had was to have the bike die and not want to run because of the 'vent tube' on the tank being plugged, and lately, when I go to switch to 'reserve', having the bike die anyway, and not start for a while until I've shaken the bike several times, waited for about 10 minutes, and then it might start and run to get me to the next gas station, otherwise I have to push it to the next gas station to fill up, which then runs fine again. I've run Seafoam through a few tanks, and that seems to solve the problem, for a couple tanks, and then the 'reserve' seems to get 'clogged' again. I probably need to pull the petcock and make sure the 'strainer'/filter on there is fine and not full of gunk or torn up, but since it's my 'daily ride' to and from work, I can't afford to have it 'down' and unable to ride.