My 12.5 briggs and stratton engine starts when choked then stalls .what causes this?

Are you turning the choke off when warmed up. Check your fuel and air filter.
Did it sit for a while?

Yefloodssrunsthensuddenlyenginestarts

Eng ine starts runs thensuddenly floods

Maybe the float is sticking, try some carb cleaner.

Try that carb cleaner or drop the bowl to clean better with SeaFoam or other good cleaners. No too hard but give the side of the carb a slight tap with a mallet.

I have cleaned the carb .now I can put the mower in gear and move a short distance but it still run high speed and I can not slow it down without stalling the engine

Drain your tank and add freshly bought fuel with a few onces of SeaFoam carb cleaner or other good cleaner. Some carbs are just very stubborn and a few could not even be rebuilt let alone cleaned.

Thanks Ill try that. When I cleaned the carb I noticed the governor spring was broken where it connects to the arm I fixed it but could the governor be the problem?

I doubt it, you fixed the spring and still have the issue, right?

Yes same problem. I'll drain the tank and get back with you. Thanks again