Since I have recently switched to a single speed from a mountain bike, I needed to buy a new pump to fit a presta valve. Is there some magical thing I should be doing to get the thing to fit right so as not to empty the tire before I get it filled? I know to open the nut on the valve, but I just couldn't seem to get the pump to grab onto the valve right. I finally got the thing to work, but what a workout! Then at one point I couldn't get it back off. I must be doing something wrong. I'm using a Serfas FP-50 on the stock tires on a Bianchi San Jose.