Just purchased an 82 SECA 750. 20K Miles, looks to be in good cond. Drove it for about 100 miles with no issues then on the interstate on a sat afternoon while accelerating to highway speed it just quit. While slowing down I tried a couple of things to get it going, no dice, a couple of backfires and nothing. It used to start immediately. Now nothing. Weird spark at the plug, like when I turn it over, no spark. Then let off the starter sw and I´ll get a spark, once. Try again and no spark then get sort of a weak spark. Any advice appreciated.