Road cyclist keeps popping out of speedplay pedals
Which Speedplay pedals? The ZERO model I used quite extensively had a pair of set screws on each cleat that would set the desired amount of float through the complete pedal stroke. 

The only reason you should be popping out of a Speedplay pedal is due to lateral foot rotation through your pedal stroke (which is really just an extension of knee/hip dynamics), or your cleat is not secured to your shoe correctly (angle of the cleat body to the release point of the pedal's design), or your cleats are installed on the wrong shoe... 

I realize this is an old question, but hope that my information might help another with a similar situation.