With S&S carbs there's a general rule of thumb for setting the mixture screw and getting the right intermediate jet. With a properly tuned bike the mixture screw will be 1-1/2 turns out from seated ( lightly, don't crank on it). Can be an 1/8 turn either way from there, if so the intermediate jet is correct size for the engine.

Warm the bike and at an idle turn the screw in till she starts to stumble, then out till if changes again, turn back to the halfway spot between the 2 points with just a hair on the rich side. Note the slot orientation on the head. Kill the bike then seat the screw counting turns. Under 1-1/2 jet needs to go down one, over go up one size. Some rare occasions due to a number of things you'll find it needs a fatter jet and will be in the 1 to 1-1/2 turn range for best performance.

With a 113" , .031" intermediate jet & 74 to 78 main is a good starting point. Been tuning S&S's since the 70's this way. And I'll warn you now don't expect gas milage to get over 32 to 35 mpg max, less if you like to play with the horsepower.

 

Does decel popping through the ex. pipe indicate a rich condition, or lean?

 

Through the pipes is fat. Try setting the mixture screw first then work out for there.