I don't have experience with CBB but have trained a lot of so call "difficult" fish. A quiet, stable, and familiar environment is more important than the type of food. It takes longer time for some fish than others. 
Also 4" is a big for CBB. Big fish is already fixed on certain foods and hard to train on new foods.  
Good luck. 
		
	
		
		
		
		
		
	
		
		
	
	
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