Briggs engine surges then dies
I have a 3 year old lawn machines mower...self-prop,6.25hp Briggs & Stratton quantum engine, series 120000. I bought it brand new and it ran fine for the first season then midway last season it would start and run fine anwhere from 2-5 minutes then out of the blue the engine will surge for about 5-10 seconds then just die. It will restart after cooling off a few minutes but I haven't been able to locate the problem and its driving me nuts! I have drained the gas after each season and replace the oil, plug and air filter at the start of each new season...using fresh gaasoline also. This problem has only gotten even worse and now the mower doesnt run very long at all before it begins to surge and die. Two days ago i removed the carb, took off the float bowl and cleaned passages as best i could and it is still surging. I even installed an in-line fuel filter and the problem hasnt changed. I have worked on cars for over 10 years so i feel confident about my work but maybe i'm missing something that you guys can help me out with?? The only thing left to be replaced is the muffler but would that cause this condition? The muffler did not appear clogged when i removed it so i have no clue what to do next. Please help..