My mower runs but after cutting grass for a minute the mower chokes down and runs like it's trying to cut off and catch up some smoke comes out by and around and through the muffler then cuts off. When I goes and pull the rope to try and start it back some gas sprays out of the exhust muffler on the side. What you think this is from?

It's flooding because the fuel valve is sticking open in the carburator.

When gasoline is stored in the mower or lines for a long time with a fuel stabilizer like Sta-bil, varnish forms on the parts. This causes sticking and or poor seating so you can get too much or no fuel conditions. As the engine warms up, the varnish gets sticky.

Another possibility is fuel contamination say from rust in the gas tank. The rust will prop the fuel valve open.

You can TRY emptying the gas and using some Seafoam carb cleaner with either some or a little gas to see if you can free it, otherwise the carb needs to be taken off and rebuilt. <$15 in parts usually.