Allowed my 1982 R100 with 30,000 miles to warm up for 15 minutes (static) then rode off and it ran OK for less than one mile at less than 10 mph then quit.  Tried starting in neutral with “START” button for 1 ½ minutes with one loud backfire, then tried again for 1 minute with a successful start.  I rode for ½ mile successfully and while rolling along at 30 mph I pulled in the clutch, switched ignition “OFF” at right handle bar grip then switched “RUN” and restarted successfully with “START” button (I did this 3 times) and motor started each time.  I rode 4 more mile with no problem until bike quit again.  Tried starting again for 1 ½ minutes with one loud backfire again.  This time I checked spark by removing plug, holding it against engine fins and cranking but with no spark.  Tried a different plug (new) and no spark.  I replaced the ignition control unit with a new unit I bought from euromotoelectrics.com, still no spark.  Suggestions from experience, please.