Small Engines (Lawn Mowers, etc.): honda gxv530 engine surges and backfires

Question
This is third carb on this engine.it is 13years old but not used that
much.mostly for leaf pickup in fall.Engine has new carb,New plugs
New air filter valves st on 4 for intake and 6 for exhaust.runs good
Under load, but surges and backfires when blade disengaged.New carb
Used to fix this problem, but not this time.Use reg grade fuel.
Thanks

Answer
If you remove the air filter and hold you hand over the carb intake throat does the engine performance change?  You will have to move your hand to open and close the air from entering the carb to see if the performance changes.  You are essentially checking to see if the engine is running rich or lean.

It could still be a dirty carb or you could have a warped carb to engine insulator or leaking gasket.

Try the hand trick to see if the engine performance changes and let me know what happens.
Eric