I just purchased a Beto Floor Pump (Dual head Presta/Schrader). I am trying to use it to inflate my mountain bike tires (presta valves), but it doesn't seem to work properly. Air is comming out of the Schrader hole - the larger opening, when I insert the presta valve in (as far as I can push it in). I have opened up the presta valve all the way (I know this as I can inflate the tube with my hand pump). Is there a switch I need to set on this pump to close the schrader valve?
My thinking is that when the prestavalve is inserted, it should automatically close the schrader hole. am I right?
On some pumps, you run the head lever down to form the seal and on others you run the lever the opposite direction. Try using the lever in the opposite orientation to the way you're using it now and see if that solves your problem.