"R" is usually used to designate a resistor plug. Out of curosity and not having working knowledge of a Fuji engine and magneto/ignition system, are there any ground wires that are supposed to be connected to anything? If so, are they connected properly and you're certain that the grounding is complete? There is probably a switch used in the line somewhere, are the leads clean and solid or could it be an old switch that has been used on a few different models? That issue comes up a lot. Do you have a bunch of servo extensions with their additional connections in the leads anywhere?

Gassers, and to a greater extent, single cylinder gassers are shakers and if you don't have everything tight, secure, and vibration proof you will encounter problems. Since you "rattled the crystal out of the receiver while breaking in the motor" I would consider replacing the receiver crystal. They should always be taped into the receiver to prevent just such an occurance. That's found in "gassers 101".