If it's the solenoid, you can pull the starter, remove the solenoid and clean it. I did that years ago on an '85 before and it's still working. You will know it's the solenoid if you don't hear any clicking when turning the key. Other than banging on it - which works but is tricky while simultaneously turning the key - a trick I learned is that with a slightly sticky solenoid, you can just stomp on the floor or move the shifter around while turning the key. The vibration is just enough to unstick it sometimes. 

Aaron
87 Westy
85 Vanaru

On Jan 11, 2012, at 6:59 AM, Ed McLean wrote:

> I had exactly the same problem with my '86.  I found when it wouldn't start
> I could whack on the starter with a 19 mm wrench hammer and it would then
> start right up.  I assumed the solenoid in the starter was sticking so the
> high amp electrical contacts were not working.  Replacing the starter fixed
> it.  No problems since.
> 
> Ed