Slant engine prob.

START sends voltage to coil side of ballast, so its a straight shot to the coil-full coil voltage, RUN reroutes 12V voltage to other side of ballast so it has to run through ballast to energize coil at a lower voltage. The hotter the ballast gets, the more it cuts voltage to coil. Here is a quote from another web page describing the ballast resistor in a Gold Wing bike:

"Catastrophic failure of the ballast resistor

This is easy to diagnose. The symptom is a bike that starts easily but dies as soon as you release the starter button. If any of you owned Chrysler cars during the 60s and 70s, you are no doubt familiar with this common problem!"