On the CFM56-5b installed on the airbus a320/321, it is common for the engine to leak fuel on start up...particularily if it is a very cold morning and its the first flight of the day. CFMI are aware of this and advise waiting a period of 5 minutes for the fuel leak to stop. This leak can indeed be quite a steady flow of fuel coming from the bottom of the engine. If the leak has not stop within the time advised, the aircraft must return to stand for investigation.
The Reason for this leak is that when it is very cold (i.e. on a very cold night...doing first flight the next morning), the seals in the HMU are not adequately warmed...hence the leakage of fuel...but soon after, i.e. using the fuel as "muscle pressure" as the HMU does, the seals return as intended..