84 FXRS Starter Issues...
On the 84's the starter is a Prestolite/ or more likely a Hitachi(shorter) strater motor. First thing is drop voltage test these three components...Starter relaysmall 1 inch plactic block w/ 4 slot holes slide onto the retainer left of main circuit breakers(located in triangle weld side), Solenoid (located to right of starter), then the starter itself. You will need a tester and shop manual or at the least a Clymer will get you on your way. Most starter issue are due to faulty ground to frame issues(negative wire to the frame), loose battery wires or corrosion, improper or grounded switch wires from handlebars to relay. The issue is fairly simple, if you hear a click-solenoid has ramped up the starter and most likely the starter may have issues with the brushes(small metal copper posts soldered to the housing(pos) and the other two metal copper posts soldered to the removable plate. This plate slip onto the rotating shaft with copper panels and if you see broken or chipped and uneven wear, this may cause hard starting problems. Other issues could be the starter wiring to brushes may by frayed due to the through bolts whichtravel the lenth of the starter to the starter housing and screw into place. You will need a retainer to secure the starter to the frame(j and P sells them they look like a C with a hole.
The starter/solenoid is a big design flaw for the FXRS(and was later improved to include both unit s into one component. Best advice is change out both inner and outter primary for a later model one-get the Spyke or All balls high out starter-problem solved. Another issue is the throwout to clutch, inspect the travel of the arm and clutch for worn teeth or broken chipped teeth(removal of primary is necessary to inspect this) on both these-if present-the rotation is not aligned and or maybe an issue with the spring, worn out bearing or main shaft... Good luck