Hopefully the note checking will reveal what the original carbonation goal was (volumes of CO2) and at what temperature the soda is being held and served.
But, in the mean time...
- Assuming the OP is now using 12 feet of 3/16" ID conventional beverage line, that's only going to be good to around 15 psi.
- Meanwhile, 40°F soda carbonated to 3.5 volumes (typical of Coke, etc)
requires ~24 psi.
-
The only line length calculator worth using says 24 psi requires at least 21 feet of that same beverage line.
The other issue: Setting the CO2 pressure below the equilibrium level (reference that carbonation table) is no cure for dispensing ills because it will cause CO2 to break out of solution, the degree set by the pressure differential from equilibrium. Bubbles beget bubbles, so the last thing one wants to have to deal with is CO2 breakout.
The order of precedence: pick a dispensing temperature, then a carbonation level, then use the table to find the right CO2 pressure to use, then use Mike's calculator to tune the dispensing system to handle that pressure...
Cheers!