Have you tried installing more beer line? I would have at least 5' of 3/16" line. There are other factors such as altitude and beer temp and CO2 levels in the beer. Generally speaking, most of what I have read is to have 5-6' of 3/16" beer line. Also, having too much beer line can lead to other problems.
From Micromatic Web site via Scott Zuhse (credit goes to him):
http://www.micromatic.com/forum/us-e...beer-line.html Post #10.
Seems that everyone is on the same page. Just to clarify, always determine what the applied PSIG (pounds per square inch gauge) to keg should be based on volumes of gas in beer, temperature of beer, and elevation. Once determined, then build in the secondary pressure that exists in the system. This pressure is experienced by the beer as it flows through the system.
This secondary pressure is often referred to as restriction and three variables in a system contribute. System hardware such as shanks, faucets, couplers and misc. hardware is one. Secondly, gravity will impact the beer as it flows and third, the one that is easily altered, would be the tubing.
If you accumulate the restrictive values of these variables and they equal your PSIG, your flow speed will be very close to 128 oz. / min. If this secondary pressure against the beer is greater than your PSIG to the keg, then your beer will flow slower.
Example: Miller Lite @ 38F @ 700' elevation @ 14 PSIG. Although all hardware has an impact on the beer as it flows through, it is so minimal that it is not worth considering. Most direct draw systems have four feet of gravity and at .5 per foot this would be two PSI against the beer. Add four feet of 3/16" ID vinyl @ 3 PSI per foot and you now have 14 PSI against the beer total. Gallon a minute flow.
With the direct draw type systems, where the keg is within a few feet of the faucet, 3/16" ID vinyl is used exclusively. It is quite powerful in terms of restrictive pressure against the beer whereas it is perfect for these "short" system runs.
Whether this value is 2.2 or 3 lbs. per foot relies on the actual ID of the line from the respective extruder and how it was tested. With the numerous years of exposure in the industry, I have often witnessed lax tolerances from tubing extruders .
This is why a recommendation for the direct draw systems would be not to get too excited about all of the math and concentrate more so on the PSIG to the keg. It is a lot more difficult to control a gas in a liquid - much easier to work with fluidtronics.
Simply start with a longer beer line - six to seven feet (longer at higher elevations) and cut back in four to six inch increments until you acquire the flow speed desired. Do not attempt this until you are confident that you have first "aligned the stars" with the PSIG to the keg! "