82 virago 920 dies after 15 minutes of riding. Heeelp.?

..#1. Take along an extra spark plug or a spark gap tester( it tests the spark energy by jumping a gap.. NOT a SPARK PLUG GAPPING TOOL!). Compare cold start up spark to hot stalling spark. If you get a different (less spark energy) spark after motorbike stalls: It's the ignition system.

#2. Remove the cap after a hot stall, attempt to restart. If it starts after... say... waiting 30 seconds to let gas run into carb bowl: It's a plugged vent in the fuel cap.

#3. If #1. and #2. do not apply take along some starting fluid; crank engine: if the motor starts and runs some 15 seconds and then runs out of starting fluid ... It most definitely IS NOT a problem with the ignition and is a problem in the fuel system such as a plugged line, plugged filter, some obstruction in the fuel tank. NOW THIS exposes you to some physical hazards... So KEEP YOUR FACE AWAY From any flammable gas ignitions, ALSO some mechanical hazards! STARTER FLUID isn't the greatest thing for long engine life! SO DON"T USE AN ENTIRE CAN!

...It's a close call between plugged vent and hot failing ignition coil. It's a bit too much time for a plugged vent and not enough time for a failing coil... but every coil perhaps has a different time line from any other coil . So my experience with... say.. 30 minutes on a failing coil really isn't applicable! ... then again; an obstructed gas cap vent will vary in engine shut down time on how much fuel/ air is in the tank: a full tank failing far sooner than a near empty tank with a larger volume of air inside the closed to outside air gas tank.

If the bike has a coil/cylinder it's unlikely that both coils are failing simultaneously (but possible) but check for spark next time it happens. Blocked vent on fuel tank more likely or almost blocked fuel filter. Another possibility is partial seizing of a piston - does engine still crank when this happens?

as others have said its most likely the coil. Coil gets hot and bike falters and dies. The bike sits and the coil cools off so the bike starts right up again. OR you gas cap isnt venting. Start her up and ride her with the cap off the bike. Obviously dont do this with a full tank. If she just runs then its time for a new cap. Or clear the vent in the cap.

What Tim said - symptom of a defective coil.

You practically answered your own question.

Feels like it's running on one cylinder - the dead cylinder has the bad coil.

Bad coils will stop working when they get hot.

They will work fine after cooling down.

When the engine will not run properly, check for spark at each spark plug cap.

You let an air cooled v-twin sit running for 45 minutes? Hope you had an industrial grade fan on it!

But yeah, check the coil(s) if you didn't toast it.

Another suggestion:

Remove the petcock and examine the screen.

Restricted fuel flow through a clogged screen can cause similar symptoms.

I had one bike that would run exactly 1/2 mile on the fuel in the carb bowls.

Often a sign of a coil failing.

Pop the gas cap and see if it still occurs - you could have a gas cap that is not venting. Easy quick and free test.

The gas cap isn't venting....it's not "the coil"