There are 3 possibilities that your wine may be foaming...
The wine is very young and carbon dioxide (CO2) is present. The pump will release this gas simply due to the action of the pump. Release of CO2 from the wine is a good thing; most kits recommend agitating the wine to help release this gas.
You have removed the port fitting (black connector on the intake of the pump). We recommend that this fitting should not be removed. If you have done so make sure that the O ring has not been crimped and that it is fully inserted into the intake hole of the pump.
The intake hose is vinyl and can expand. Cut approximately 1/2"" to 1"" off the end of the hose and re-insert the hose. This will create a better seal at that point and not allow any air intake.