I have a Craftsman mower with a 6 h.p. Briggs&Stratton engine. The mower has set most of the summer and when I went to start it today it started on the first pull and then died. I tried starting it several times and had the same result. I took the carburetor apart and cleaned it and never saw any trash. I put it back on and it cranked the first pull and ran a few seconds and then it seemed to run out of fuel and died. I put a new fuel line on it, took the tank off and cleaned it and refilled it. When I started it then it ran for 2 or 3 minutes and then acted like it ran out of fuel again. I found out that I can take the fuel line loose at the carb and immediately put it back on and it will crank and run briefly and then it slowly dies again. I also gave it a shot of carburetor cleaner in the air filter and it cranked and ran for 5 minutes and then died again. I have loosened the gas cap while it is running but it does not help. Anyone who has advice about what this could be, will be appreciated. Thanks in advance.