I had almost the same problem the other day. I was out brush hogging when my DX33 died out on me. I tried to restart it /forums/images/graemlins/mad.gif /forums/images/graemlins/mad.gif, no go.
I looked at the fuel level and it was higher than when I had started, so I took the fuel cap off with a release of the vacuum the level dropped from 3/4 to 1/4. After that it started right up and ran fine.
When I got back to the house I cleaned out the vents in the fuel cap, hopefully that will solve the problem.