throtle setting not high enough, bad spark plug,
Something else to check
Newer mowers come with a safety interlock system that prevents mower engagement when no operator is on the seat or when the parking brake is engaged. Check your seat switch by junping across the terminals, if the blades start then the seat switch is bad.
This is usually caused by a faulty seat safety switch.
a stall will not engage trans until a minimum rpm is reach depending on rpm range of the stall converter
The seat safety switch is not working properly correctly. If the safety does not sense that there is anyone on the seat then it will shut down the mower. This keeps the mower from running over someone if they would happen to fall off while mowing. Or if the safety is working you may have bad bearings on your deck and that will also stall your motor, or something jammed in the blades.
My weed eater lawn mower was expose to the wet weather and now it not staying on
Retreating blade stall.
The engine can't handle the extra load. Check the spark plug, fuel filter and air filter. If all is okay, open the carburetor needle valve (rotate counter-clockwise) 1/8 turn for a slightly richer mixture.
Typically this is caused by a bad seat safety switch.
There are two things that could cause this. The first and most popular problem is that the safety switch for the seat is not working correctly. It determines whether someone is on the seat. If for some reason the driver should fall off of the mower while mowing it will shut the mower off. It is a good feature but it causes the problem you are talking about when it fails. The other thing it could be is a problem in the deck. One of the spindle could be seizing and keeping the deck belt from turning. That would bog down the engine and make it stall. This is rarely the problem. You can rule this out by taking off the deck belt and starting the mower, lowering the deck and see if it still shuts off. If it doesn't then this is the problem.
Helicopter blades act in the same way as the wings of an airplane. They generate lift with the air flowing faster on the top of the airfoil then on the bottom. When you reach a certain speed, depending on blade specifications and limits, the air flowing over the blades become equal on the top and bottom of the airfoil. This is what is known as blade stall. The blades no longer generate lift. The same effect in fixed wing aircraft is known as a speed stall. This concept also takes place when a helicopter flies too high. As the air thins with altitude eventually there is not enough air for the blade to "bite". Thus blade stall again.
Check the gas tank for water at the bottom of the tank. That is a common problem.
Dirty carborator. If its been sitting for awhile the carborator collects dust and other crap in there and clogs it up.
Because on a manual if you don't shift the gear doesn't engage and you stall. That's why people all over the world use automatics more. Because they're too lazy to shift or are too sccared.