What is your actual setup now? It sounds like you want to get the thing to rotate more off power. The b3.1 car can have a TON of off power steering. I actually was taking some out.
A 1/8 buggy that is pushed by the rear end is going to understeer. It also can't be driven like a 1/10 buggy, as I'm sure you are aware. It sounds like you may have been trying to get your desired result the wrong way.
What rear sway bar are you running? It sounds like you may need a bigger one, and perhaps more rear spring to start.