I have a topeak mini master-blaster hand pump, that works with both schrader and presta valves. It took me a while to figure out that I had to flip a little rubber piece in the pump to make it work with the presta valves, but I am still having issues. It doesn't seem to want to lock on to the valves securely, and whenever I try to pump up the tires I seem to end up losing more air than I am pumping. Does anyone know how to make this work?
Thanks in advance.

The tightness of the grip generally depends on how much the washer has been squeezed to start with and that depends on how tightly you screwed on the nut that secures the washer. If the washer is pretty loose, it wont have a chance to grip the valve. I am not familiar with the particular pump, just speaking from general experience. Otherwise, are you properly operating the lever, putting the head on first and then raising the lever?

sonac36: I don't know for certain about your Master-Blaster, but my Road-Morph G requires you to flip BOTH the rubber gasket AND the plastic valve depressor to switch from Presta to Schrader. You might want to review the instructions for your pump.

And good luck getting help from Topeak. They used to be awesome but i had a mountain morph that came with a bad plastic piece inside but since I NEVER wanted to use it presta, I never noticed. That is until I noticed. I called Topeak and put in a trouble call. no return. emailed. nada. Luckily I found a piece for it at my local coop. I'm sure I'll still buy them but I'll be sure to check the status first!