The ground is normally achieved through the braid and spark plug cap however adding another ground wire from the CDI to the engine wont hurt. Make sure your plug is an "R" type - resistive. This is normally identified by an R in the spark plug number. Ensure no metal to metal contact - I see you have already addressed this on the throttle linkage, and place the Rx as far away as possible from the CDI. Whether using PPM, PCM or 2.4 - make sure you address these issues as PCM or 2.4 will only mask the problem - not solve it.