Many guys have gone with the single cable setup, no return cable without backfiring. So while it needs adjusting I don't think this is your problem. The adjustments are made at the top of the bracket surrounding the "horseshoe" or quadrant for the throttle cable and also at the upper end of the throttle cables near the handgrip. Adjust the pull side first leaving about an eights inch of rotation on the handgrip before the quadrant rotates. Then adjust the return to about the same tension. If it drags its too tight.
What do your plugs look like?
Is the idle smooth?
Have you done any other mods: ie jetting, pipes, intake?
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...