RE: Which brush less motor?
Raz, what batteries are you running?
If you're running the stock batteries that's your problem. The Mamba needs premium cells with premium connectors. You need to get GP1100's, or run lithiums. GP1100's are your best bet. The pack has to be assembled with battery bars, not thin, spot welded tin and use Deans connectors.
If you don't use top quality batteries with the Mamba it'll never work right.