AFTER TAKING OFF ON A TEST FLT, THE PLT REMAINED IN THE TRAFFIC PATTERN & WAS ON DOWNWIND WHEN THE ENG SURGED OR SPUTTERED, THEN LOST POWER. SOON THEREAFTER, THE ACFT ENTERED A STEEP DSCNT & CRASHED. THE EXPERIMENTAL, HOME BUILT ACFT HAD ONLY 11 HRS OF FLT TIME. NO PREIMPACT PART FAILURE OR MALFUNCTION OF THE AIRFRAME WAS FND. HOWEVER, DISASSEMBLYOF THE ENG REVEALED THE BREAKER POINT MOUNTING PLATE & MACHINE SCREWS (BOLTS) WERE LOOSE. THE BOLTS HAD BACKED OUT OF THE THREADED HOLES & WERE BENT. ONE BOLT WAS LODGED BTN THE FLYWHEEL & THE ENG HOUSING, RESTRICTING ROTATION. THE LOOSE BREAKER POINT MOUNTING PLATE WAS PART OF THE IGNITION SYS. IT HAD BEEN INSTALLED ON THE ENG HOUSING WITH 2 BOLTS, WASH- ERS & LOCK WASHERS. RPRTDLY, THE LOCK WASHER(S) HAD BECOME FLAT, INDCG LOSS OF ELASTICITY (LOCKING ABILITY). PREVIOUSLY,THE FLT CTL SYS HAD INSUFFICIENT ELEV CTL AT HI & LOW PWR SETTINGS; TO CORRECT THIS, AN ELEV SPRING WAS INSTALLED & THE ELEV CABLE ATTACHMENT BRACKET WAS REPOSITIONED, BUT THE PREIMPACT COND OF THE ELEV CTL SYS WAS NOT VERIFIED.