I have a sears craftsman dlt 3000 with b&S 18.5. while at idle or full power (no load) , the engine gallops. WHen I engage the blade, it runs fine.
I have replaced both air and fuel filter, spark plug, ran cleaner through the carburator. Tried adjust via the one screw on the carb, and cleaned the flywheel, still no luck, it still gallops.

Any recommendations??

Try cleaning the carb. Sounds like there is a microscopic piece of trash in the carbs jets. Be sure to clear the holes inside the throat on the side which are located behind the welch plug on the outside of the carb body.