68 coupe, 302 4V, runs good til I turn around.

[69Markstang]

I ran the car a 1/4 mile up the road. When I turned around at the Y (a counter clock wise circle), it started running bad. I had to nurse the throttle to make it home. I did a tune up and set the timing. (plugs, wires, points, rotor, cap)
I started it up and it sounded pretty good. I drove same route and wierdly enough, the same thing happened. Was running good until I turned around, same place same pattern. Limped home.
The car has a new gas tank. It has an inline, clear fuel filter. It looks fairly clean but is completey full of gas. It seems like it was always half full before.
Another note is that I have to jump the battery each time to start it. It wont hold a charge. I will get a new battery soon.
Any ideas?