I'm assuming the mower is new.

The gas should be fresh, i.e. purchased in the last 30 days. If not replace the gas. Are you trying to start the mower with the blades over uncut grass? If so, move it to concrete or an area where the grass doesn't touch the blades. If none of those are issues, the vent hole in the gas cap might be plugged.

Does it have a manual choke? If you leave the choke on, it could exhibit what you describe. Also, if the butterfly valve that actually does the "choking" is sticking closed, whether it is an automatic or manual choke, it could cause this. Remove the air filter. You should be able to look inside your carb. If there is a solid piece of metal closing off the throat of the carb, your choke is on. That metal should turn and open up the throat of the carb when the choke goes off. If it doesn't, that is your problem.

Also check the Oil Dipstick Level if it appears unusually high smell it , does it smell like gasoline ? Your needle valve may have stuck causing flooding into the crankcase. If no gas smell but have high oil level , then the oil is being sucked into the breather , causing the white or bluish white smoke on startup . Check it out and let us know .

A mower that is that new must still be under warranty. There is where you want to go for repair.

Otherwise, when you ask for help on an engine, the model number of the engine is usually a prerequisite to getting a good diagnosis.

Walt Conner

The air filter is contaminated by oil either by tipping improperly or overfilling with oil. Remove the filter and reset the oil level as needed. Clean the area around the filter and replace it. The smoke should clear in a few minutes of running.

cutting out and gets very hot too. Mower is not new, but starts great and runs great when runs. What is happening? I am going to check gas cap and will check filter, and what else should i check/do?

Same with an automobile....
At the "cut-out" event, remove the spark plug.
Is it wet or dry ?
If dry, why ?
No fuel, so back track to the fuel delivery system, including the gasoline itself.

Hi I made a dvd to cover the exact problems you are having. If your interested you will find it here.
Hope this helps.
http://www.repairinglawnmowersforprofit.com/
P.s The DVD is also available at ebay.com under the title Briggs and stratton repair manual dvd video.
Its a very simple to follow dvd and should help you sort this small problem out.
Kind regards
Stampy

Here is a link that might be useful: Repairing Lawnmowers For Profit