The only 1/2A engines that need either a bladder or backplate pressure to run consistently are TDs with enlarged venturis or AMEs. IMO the way to go is use stock AP or BigMig .061s, they have plenty of power without raising the planes' performance to the point where you are having a demolition derby. Guys who experience trouble with these engines probably don't add a few ozs of castor to a fresh gallon of store bought fuel. I just buy 15% nitro, add castor to it and use it for everything I own.