Okay, keg is at ~38°F, pressurized to 24 psi, which BeerSmith says should give me the 3.7 volumes of CO2 I'm looking for. (The gas tank is in the mini-fridge as well, if that matters.) Ten feet of 3/16" vinyl tubing on the output, ending in a Cobra picnic tap. It seems the tubing restriction is right around the 2.2 psi/ft that Tom mentioned earlier, because the flow rate at the end is about 2 oz/second, which I understand is about ideal for a tap setup.
The problem is that even though the pressure and flow rate are correct, I'm still getting mostly foam when I pour. I'm starting to wonder if it has to do with the sweetener in my soda syrup, since I know commercial diet sodas tend to fizz up more than their corn-syrup-sweetened counterparts. (This particular syrup uses Splenda.)
Any ideas how I can fix up this last little problem?