17hp b/s intek OHV after 30 min mowing starts running rough

my thought is the valves are out of adjustment. that is the popping you hear or backfiring. i think if you take off and clean the carburetor and set the valve lash it will probably run like a new one.

muffler full of carbon remove muffler heat up red hot throw in bucket of cold water remove and throw as hard as you can on pavement clean carbon out of exhaust part of headt make sure piston is all the way up you dont want carbon in your motor reinstall thank me

clean the carb you have a dirty idle circuit

0.030

the coil that attaches to the spark plug wire may need a replacement for usually when they get old the heat will make them weak after the engine is running causing a problem such as yours here

Just maybe, since this is an OHV engine, the valve lash needs adjusting. Your are possibly seeing the results of poor clearance when the machine heats up and the metal valve train expands, Then after cooling, the train is within tolerance again, allowing the engine to start and run. Check into adjusting those valves.

The condensor is not the problem for they go bad upon not hold a charge. When the engine heats up and the engines dies out the problem may lay in the magnito's frame mounting from swelling from the heat, a loose mounting bolt(s). Or a Magnito that is ready to go out completely

could be fuel vaporising.... re rout the fuel line away from heat sources this may help or the fuel is not getting to the carby fast enough....check fuel filter and lines for cleanness .

Could be valve hanging, need to check compression when hot.

My first thought is that the throttle lever is being pushed so far forward ( max RPM's ) that you are running the engine 1/2 or better choked
Look at the choke butterfly with the throttle in your normal run position it should be completely open
This may require and adjustment in the control rods or might be as simple as not pushing the throttle wide open