THE INSTRUCTOR (CFI) RPRTD HE PREFLIGHTED THE ACFT & TAXIED TO THE REFUELING AREA. WHILE THERE, HE WAS APCHD BY ANOTHER PLT WHO WANTED TO GO WITH HIM ON THIS FLT. THEY AGREED & THE CFI MOVED TO THE RGT SEAT. THEY COMMENCED THE START-UP, RUN-UP & TAKEOFF CHECKLIST. THE CFI RPRTD THAT AFTER CLIMBING ABOUT 150', THE ENG LOST POWER. A TURN WAS MADE AWAY FM BLDGS & HOMES FOR AN EMERG LNDG IN A FLD. JUST BFR REACHING THE FLD, THE RGT WING HIT THE TOP CROSS PIECE OF A TELEPHONEPOLE, THEN THE ACFT CRASHED TO THE GND & WAS EXTENSIVELY DMGD. THE PLT RPRTD THAT JUST BFR IMPACT, THE ENG STARTED TO REGAIN POWER. AN EXAM OF THE ACFT REVEALED THERE WAS MOISTURE IN THE CYLINDERS. THE LEFT FUEL TANK CONTAINED FUEL WITH NO CONTAMINATION, BUT THE RGT TANK HAD RUPTURED & FUEL HAD SPILLED OUT. A CHECK OF THE RGT FUEL CAP REVEALED IT WOULD ALLOW WATER TO LEAK IN. THE BOLTS HOLDING THE CAP WERE TOO LONG & THE CAP COULD NOT BE ADJUSTED FOR A TIGHTER FIT. THE MIXTURE CTL CABLE HAD PULLED OUT OF A FITTING ON THE CARBURETOR, BUT IT SHOWED NO EVIDENCE OF SLIPPAGE BFR IMPACT.