There is a lot of BS still floating around about interference on 2.4.
The fact is the only way you will get interference is if the entire band is wiped out. That can happen if there is an unshielded spark somewhere.
An external ignition depends on the shield to provide its ground. If you break the path you will get that spark. The way to fix it forever is take a bare wire and wind it tightly around the shield then ground the other end to the motor. Then you wont have to worry about a loose cap.
BTW a toroid is very effective on 2.4.
.
It is even more effective than on 72. It is just not needed