Craftsman Lawnmower Stall after running a few minutes

[dce]

My Dad has a Craftsman Lawnmower. It is a 6.5HP Briggs and Stratton engine. It stalls after running a few minutes. It maybe 20 mins or 2 mins.
It started last year. The mower had set up for about a year and a half. I started it, but after about 5 mins it stalled and gas was coming out of the primer bulb. I rebuilt the carb., and ever since then we have the stalling issue.
I have taken off the carb several times and cleaned every nook and cranny with carb cleaner. It has a new spark plug and air filter. We have also changed the gas.
Any ideas what may cause this?

 

[ILENGINE]

Make sure the fuel cap is venting properly, provided it isn't one of the new charcoal canister caps.

 

[FloGro]

Does it start back up and run after it shuts off or is it hard starting and shut right back off when it turns over

 

[dce]

I tried the fuel cap from my lawnmower, which is similar, but it didn't help. Sometimes it starts right back, and other times it is a little hard to start.