I have been having problems with the set-it-and-forget-it method of force carbing my corny kegs. I used to brew 5 gal batches, and had 2 cornys. I have a double manifold on my single-regulator CO2 tank, and would drink from one keg, while the other carbed. Left it at 12 PSI @ 34F all the time, no problems, and it seemed like my kegs would always be carbed and ready to drink in 5 to 7 days.
Well about 4 months ago I moved to 10 gal batches and bought another corny. I also bought a T and another gas fitting for the corny, and plumbed that off one side of my manifold, so I can have 3 kegs attached to the tank now. I schedule my brews so when 5 gals of one brew is gone (drunk or bottled), I can fill up 2 kegs with a new 10 gal batch and let it carb. However I am now finding that it is taking about 14 days to properly carb the new kegs, still at 12 PSI and 34F. Is this because I now have three kegs on the gas? Or because of my T splitter feeding the two uncarbed kegs? Or does carbing take longer as the gas cylinder gets empty - I think mine is getting empty because it's been going forever, but the gauge still shows the same tank pressure as when it was new.
In a related question, I now have 10 gals of a Brown Ale that is 11 days old in the primary... I was hoping to be able to rack it into the kegs this weekend, but my current beer is not carbed yet, so I can't bottle it as I planned to.... so how long can this ale sit on the yeast in the primary... it was down to final gravity at 8 days, so it is ready to keg.