I have a briggs & straton 6.25 hp self propelled lawn mower bought at sears. It's probably 4 or 5 years old. The mower starts but when it warms up for about 5 or 10 minutes it shutts off. I removed the carb and sprayed it with carb clnr and put it back and still doing the same thing. I noticed that if I spray some carb clnr on the inside of the carb the engine runs, but when in stop spraying it shutts off. Do you think it needs a new carb or is it internal in the engine?

Try cleaning the lines and fuel filter

I would say carb probably needs cleaned,but some of those carb are cheap enough its not worth trying to clean it.

Also check the gas cap, if it's not venting correctly, a vacuum will be created in the tank and fuel starvation will occur, usually in 5-10 minutes. Just crack the cap open a hain and see if that solves your problem.

I have a briggs 6.25 hp on a Sears self propelled lawn mower. I cleaned the filter, carb, and the fuel bowl and still sputtering. My daughter was the last one to use it so I had just about resigned myself to flywheel key replacement.

I noticed that the throttle control was governed and the cable is fixed lever so you can only run in one speed. I manually pushed and held the throttle to the wide open position and no more problem. On further investigation, I discovered that the throttle cable attaching clip on the right side of the push bar assembly had come unlocked. I snapped it back in place and the throttle could now be opened using the throttle lever at the top of the push bar.

99% of all trouble is the simplest thing. When will I learn... add adjust or check throttle linkage to the list of usual suspects.