Sears briggs and stratton 5hp 10t800 engine starts but dies immedietly

[milesd3]

I bought a used mower last year and have had nothing but trouble from the thing. It turned out that the intake manafold had a crack in it near the hear (cheap plastic part). So when I finally got that figured out the mower worked the rest of the year but with problems toward the end of the year. First of all it didn't seem like the pump was working corrrectly on the carb so I replaced it but taht did nothing. The lawn mower would start and run fine if left running (just sitting in the yard not moving) it could run the tank dry but if I put even the stightest strain on it it would die. it sometime would die when I lifted the front wheels up??? I changed the gasket and diaphram last year and it didn't seem to do anything. Same problems this year. It took almost 3 hours to mow my lawn which normally doesn't take 45 minutes! Sooo yesterday I replaced the diaphram and gasket and the primer again and now it starts after pumping the primer 10 15 times but dies right away. There seems to be no adjustments on the carb itself so I'm at a loss as what to do now? Help my yard is going to be knee deep soon!