Tom,
Could very well be a poor ground to the starter.
Try grounding it to the frame somewhere where it's clean.
If that isn't it, it might be the neutral safety switch,( if automatic )
or last but not the least, the ignition switch.
I had similar problems a while ago, and it was the ground thing, after I
replaced everthing else, ( starter, ignition switch, neutral safety
switch, wiring to starter from neutral safety switch )
I ran a 8 gauge wire from the bottom starter bolt to a hole in the frame
I drilled.
Poof! No more problems!

Good Luck,

Terry

85 GL