Small Engines (Lawn Mowers, etc.): 214 JD, Engine boggs down after 30 mins. of running, kohlor, vent hole

Question
I have a 214 John Deere, 14 HP Kohlor. Starts good, after running at 1/2 to 3/4 throddle for about 30 mins, engine boggs down like it's starving for gas. I cleaned carb. set both adjs. to 2 1/2 turns. new air filter. New fuel pump, fuel lines, filter and cleaned strainer on shut off valve at tank. Still boggs down, gas cap vent hole OK. When boggs down, engine pings like it's hot. Washed engine to make sure air is circulating good. Still same issue. Not sure what to do next. Could any part of the engine be cracked and opening up as it gets hot? Need help. engine is a K321 Kolhor.

Answer
 Hello Raymond:

 Remove the Muffler and Check the Exhaust Port and Muffler. They could be Stopped up. Also could be a Valve problem too. Set the High Speed Fuel Mixture Screw to 2 instead of 2 1/2 turns. Hope this Helps.

 Good Luck

 Respectfully

 John