THE HELICOPTER COLLIDED WITH TERRAIN ON A WOODED MOUNTAINSIDE AFTER LIFTOFF. THE PLT SAID A POWER LOSS OCCURRED AFTER ITWAS TO LATE TO ABORT. TAKEOFF WAS MADE FROM A LOT THAT WAS 5200 FT MSL. THE PLT HOVER-CHECKED AT 2500 RPM AND 39.5 INCHES OF MANIFOLD PRESSURE PRIOR TO TRANSITION TO FORWARD FLT. THE ACFT CLIMBED ONLY 20 FT BEFORE POWERLOSS OCCURRED. THERE WERE NO CHIP LIGHTS OR UNUSUAL ENGINE GAGE READINGS. THIS WAS THE PLTS 65TH TRIP FOR THE DAY. DURING THE IMPACT THE THE RIGHT LANDING GEAR COLLAPSED. DURING THE INVESTIGATION THE COMPRESSION WAS FOUND TO BE LOW ON 4 CYLINDERS, TWO OF WHICH WERE ZERO. TSO WAS 573 HOURS. THE CARBURETOR INLET SCREEN WAS PARTIALLY BLOCKED WITH FIBER LINT. COMPRESSION WAS BEING LOST THROUGH THE EXHAUST VALVES. FUEL FILTER WERE PARTIALLY OBSTRUCTED WITH CONTAMINANTS FROM FUEL DRUMS AT A WORKSITE.