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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?

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

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

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.