Hiya, just got back in the game with another FB. 1984 GS 150k almost entirely stock. Drove fine for a few weeks, started making her mine and taking care of all of the little things the previous owner did not. One day, about 1/2 way (10 min) on the way to work, she started sputtering and dying and i barely made it to work. Started her up fine when I went to leave work, and again about 10 min into my drive she started sputtering and dying.
I thought it was fuel related, so I rebuilt the carb (had a small leak from AP gasket anyways), same thing happened. I pulled the fuel hose off the carb into a cup; the fuel came out clear and quick. I'm starting to think this is ignition related. Can ignition parts start fine and then start to die with heat? What should I look at next? Ignitors? Coils? Emissions?

 

fuel filters are cheap enough so you can probably go ahead and replace it (just in case), but i'm thinking it's probably a dying fuel pump.

 

Check the coils per the FSM or Haynes.

 

Mine did this too. Start up, drive then it would die after a few miles. Sit for 5 min then started fine, ran well, briefly, then died. This only seemed to happen when tank was 1/2 full or less...
Turned out the fuel tank was shedding corrosion into the fuel exit hose in the tank. Would get sucked up to hole, plug it, stall out. Once dead, gunk would settle away from hole, allowing fuel to flow again on restart till it got sucked back. Repeat.
Pulled tank, took to rad shop for pro chem dunk, then POR15 tank seal kit'd it and reinstalled. Prob solved.
And yeah, do swap in new fuel filter FIRST and see if that does it. These should be religiously changed every year.
'luck
Stu Aull
80GS
Alaska

 

I had a similar experience. The tank on my car had been coated sometime in it's life and the coating was coming off and clogging the pickup tube when the fuel was low.