Why is my 450 series 148cc briggs and stratton lawn mower engine running fine and then when it gets hot it runs with no throttle

There are multiple mower manufacturers with Briggs & Stratton 450E engines. For specific instructions you need to provide the mower manufacturer model number.

Likely there is no throttle cable which means the mower always runs at speed, i.e. no idle speed. This means engine speed is set by bending a fixed metal tab, see attached photo item 222. Bend tab 222 to increase tension on governor spring item 209 to increase rpms. Reduce spring tension to lower rpms. It maybe necessary to remove the air filter for access to identify and adjust the tab.

The 222A assembly shows a pivoting tab used when a throttle cable is present. Otherwise the tab is fixed to a similar bracket.

Find Your Operator Manual Briggs Stratton Go here to get the maintenance manual for your engine.

check your cork washers to your carb

best place is from a B&S mower shop. Try e-bay as well as they are available on line. may be you know some one who has a mower that is not going that you can get the unit from it.

Hi Travis

Standard oil for the briggs engine is an SAE30 grade

main jet clogged and use plain 30 weight oil in it not not 10w30

More than likely, it is the main jet is partially clogged. That is the brass bolt that holds the float bowl onto the body of the carburetor. Remove this bolt and washer and clean it well. Use no metal objects to clean it.. Make sure the bottom hole and the side holes near the top are clean and clear.Carb/choke aerosol spray should do the job here. Use no metal wires or scrapers on the jet. Clean until shiny, reinstall and try starting the machine.

Your throttle cable likely needs adjusting.
It should be fastened on the engine with a screw. Loosen that screw and adjust while engine is running then tighten Keep fingers away from underneath while engine is running.

Not getting gas