7.8 HP 4200 WATT AC GENERATOR-MODEL 580.327141 ENG SURGES?

GEN IS STORED IN A UTILITY ROOM-ONLY USED WHEN POWER IS OUT-CHECKED OIL LEVEL-O.K.-I FOUND THE FUEL WAS BAD, CLEANED FUEL TANK, TOOK CARB APART, CLEANED, HAD SOME WATER IN IT-STARTED ENG-RUNS FINE AT 1/2 CHOKE, PUT UNDER LOAD RUNS O.K. AT 1/2 CHOKE-OPEN CHOKE TO RUN-ENG RUNS BETTER, ONLY SURGES SOME TIMES, PUT UNDER LOAD AND ENG STARTS TO SURGE AGAIN-I CLEAN AND SET THE SPARK PLUG, ADJUST VALVES TO SPECS-SAME PROBLEM-DO YOU THINK I MIGHT HAVE A BAD CARB?