After the mower gets hot, it shuts down.

Maybe some thing in the Carburetor or plugged fuel line? Worth a check

It's one of two things. My first thought is that you have a clogged gas cap. Try loosening it when the mower starts to run ruff. If it smooths out again and runs fine, then you know that the carburetor is not venting properly. Either buy a new gas cap or clear the breathing holes in the cap, if possible.

The only other thing it can be is that your Ignition Coil is going bad. A bad Coil, once it gets hot, will shut down. But it usually takes longer than 5 minutes for them to cool down well enough to start back up.

My Vote is the cap!

Good Luck!

Jim

Your ignition coil is failing when it gets hot.make sure the cooling fins on the flywheel are not plugged up.you will probably have to replace the coil.

When it shuts down check it for spark. You sound like you may have a weak coil. OR

You might have water in your fuel and it only runs until it hits the water level in the carb. You can try draining your carb *(do this when mower is cold...never drain gas from a hot mower!) and see if the mower runs longer. While you are draining your fuel you can check the float level too. A float that closes too early or that is partially obstructed might only let in enough fuel to run for short periods. Then, your three minutes of sitting is just to let the carb bowl refill. When you remove the carb bowl let the float hang down and note the fuel flow. Is it fast? Or is it just a slow drip? If it seems slow you should work the float up and down a few times to see if the flow improves. If it does improve consider draining all the fuel out and cleaning the gas tank.

Good luck and be careful!

your carburator is gummed up. get some fuel additive called seafoam. Add it to your fuel and run your mower for a few minutes. this should clear your problem. if it doesnt you will need to rebuild the carburator. J.

There is no fuel filter, maybe a screen in the tank. Running good for 20 minutes then shuts down sounds like a coil getting hot then not sparking. Next time it quits check for spark.

The two most likely suspects for the symptom you describe are:
a) Ignition coil failure under high heat.
OR
b) Decompression failure due to normal wear.

For a positive diagnosis try the following:

For scenario a)
Run the engine until it shuts itself down. As quickly as possible, check for spark using a spark tester (availabe at local auto parts store). If no spark when hot, allow to cool down and test again. If good spark when cold and no spark when hot, change the ignition coil.
Proper part number (assuming your machine is still all original) Briggs & Stratton part #492341.

For scenario b)
Run the engine until it shuts itself down. Try to restart but pay close attention to the speed of the spinning starter. Next, remove the spark plug and spin the engine over (WITH SPARK PLUG WIRE WELL OUT OF THE WAY!!) If the engine spins super fast and free you can discount the theory of a bad battery and you will need to adjust the valve lash.

Determine which is the case and reply to this post. I will gladly give a detailed explanation of the valve lash adjustment procedure in another post.

Hope this helps!

sounds fuel starvation check the filter or the vent into tank is causing a vacumn

The plug is breaking down.Change the plug.

I WOULD LOOK FOR AN ELECTRICAL (IGNITION) SHUTDOWN,CHECK WHEN IT SHUTS DOWN WITH SPARK TESTER TO SEE IF IT IS FIRING.