Walk-Behind Mowers

I purchased a Weed Eater Walk Behind Push Lawnmower, Model # 96114001505, Serial # 022311M-011300, on May 6, 2011. It has a taller gas cap than others. My Wife bought the same model as mine, but with the normal type of gas cap.
When we both mow, for maybe 15 minutes, at the same time, my lawnmower starts loosing power, and wants to quit, then does quit. When I try to restart it, it squirts gasoline out the hole at the top of the gas cap, like a squirt gun!
My Wife's lawnmower doesn't have any problems! Her's works perfectly, no matter what!
Mine just quits, and squirts gasoline when I try to restart it!

We both bought our lawnmowers at Walmart East, Green Bay, WI, on May 6, 2011.

What is wrong with my Weed Eater lawnmower?
Did the factory have the valves adjusted wrong? Or what?

The lawnmower is still under warranty.

Oh, after letting it cool for about an hour or so, it starts okay, and lasts until as above, then does the same thing.

That appears to me to be unsafe? Has anyone else had the same problem?

I Need to know, should I take the lawnmower in to an authorized dealer?

This never happened to me before! We both take good care of our mowers, and store them in the garage. We always use fresh unleaded gasoline, and check the oil, too! After mowing, we always clean the grass clippings off the mowers with a brush.

Please, your help and assistance is needed.

Thank you!