A PA-32 Saratoga's mechanical fuel pump apparently failed and caused a power loss during climbout after takeoff. An emergency was declared by ATC after the pilot requested a precautionary return to land.

Narrative

The aircraft had undergone extensive work for the last 2 months. This was to be a test flight to make sure the new avionics were working properly. We took off on the short runway because the main runway was closed for pesticide spraying. We had not used this runway before in this aircraft; but I was not concerned because we had taken off from shorter runways in the past. However; from the time of takeoff things did not feel right. We barely missed the trees on takeoff and the aircraft was laboring to climb. At an altitude of 2500 FT we leveled off and immediately began feeling and hearing surging in the engine. We notified the departure airport Tower that we wanted to return for a precautionary landing. At that time we also requested the longer runway; which had recently been closed for pesticide spraying. We then returned without further incident; resulting in a normal approach and landing. Upon landing we were informed that the Tower had declared an emergency. The only thing I would have done differently is perhaps put off the test flight until such time as the longer runway was available again. However; it is unclear that this would have helped in this particular situation. At this time; the mechanics still have not determined the cause of the loss of power. However; our working hypothesis is that the mechanical fuel pump may have failed.