Motorcycle Repair: harleydavidson shutdown, flt, spark plug

Question
I have a 1988 flt that runs great for about 20 or 30 miles. Then the bike will sputter and sometimes backfire, and then just shutdown. If you try to start back up immediatly the bike will just turnover. But if you wait about 30 seconds the bike will fire back up and run good for about a mile, and then shut down again. The longer you let the bike sit there the farther it will run before it shuts down again. Can you give me somekind of insight on what the problem is. Thank you

Answer
Ride the bike and when it shuts down pull a spark plug and see if its getting a spark. If you are not then you need to test the coil. Coils can fail when hot. If the coil tests ok then check the ignition pickup. It can also fail when hot.
Good luck and happy riding
Mike