Sounds like youre running fine at 42 mpg. Most of us are around 40 with mods, but you tend to get more in the throttle the better it sounds. The smileage factor! Do you have the AIS disconnected? Mikuni the builder of your carb says that some crackling and popping from an open exhaust is considered normal in a performance/open exhaust. The Mech/Dealer was trying to drum up business. If it ain't broken don't fix it. Your plugs should be a light tan for optimal.
2005 1100 Custom
ORKed 5/16" Lines
PODs K&N RU-600s W/PCV
PCS XXX/2 cams
Jetted & PMS Tweaked 20.0/152.5 3.0 turns
Wimmer Machine Custom Oil Cooler & Stash Tube
Dyna 3000 Step 5/ 6500 redline
6" Fwd Control Extension W/Boards F&R
Memphis Shades Bullet Fairing
Progressive 465 rear
Progressive Springs and GVE front
10,000 Monkeys throwing crap at the glass and this one thinks he's Picasso...