problem with V-twin e-revo

Just installed 2 VXL systems in my dads E-revo. We followed a guide from the traxxas forum and its all linked up as the guide says, but we cant get the systems synced. Both ESCs are on, but only 1 motor is running, weve tested each system and both work indidually, but just cant get them to run together at all. Any help would be much appreciated.

thanks

Ant