I used to own a 1980 Suzuki GS850GL, and I've read a lot of controversy regarding jump-starting motorcycles with cars/car batteries for that particular motorcycle. The general consensus is that it is unwise to do so as the load the much larger battery will draw on the Regulator/Rectifier to continue charging the battery can burn the R/R out.
I know the older Jap/Brit bikes (especially the GS series) were notorious for sketchy R/Rs (I was warned against installing heated grips...) but I was wondering what your thoughts are on jumping the 14?