Spotty/porosity tells me two things... 1) contamination of the base metal or filler metal and/or 2) shielding gas is improperly set. Too much shielding gas can cause turbulence in the flow and allow atmospheric gases/O2 into the weld area causing porosity instead of preventing it. Too little gas, same scenario.
Most guys set a regulator and never look at it again until they start having issues.... Check it before you weld EVERY TIME! I do it 2-3 times a day. Also, a new/full bottle will yield around 22-2600psi, the cheaper regulators tend to "bleed" more pressure/gas, you may have a really nice Victor (or similar) set up and not your issue at all. But, seals, rings and other components wear out over time. Gauges are even worse with cheaper set as well.
I weld with .035" wire and usually run around 14-20 CFH.
Set your regulator at 15CFH and then turn it up/down from there until you like the results.
J