This issue has been happening for about three months now. At first I thought the carb could use a rebuild but now I am a bit worried that this is a transmission issue with my TH350 in a 68 Cutlass Supreme. When going uphill and having the pedal depressing about half way down, the car will go up to 40mph very smoothly and then start to jerk between 40-50mph. It feels as if the engine is firing, then stopping, firing, then stopping. The video gives you a pretty good idea with sound. If I give it more gas it will take off fine. Once it starts to jerk it picks up speeds in small increments. Thank you.

http://www.youtube.com/watch?v=RKSrnmSpq6M


p.s. Ignore that the gas gauge says empty. The fuel gauge doesnt work. There is gas in the car.

 

Sounds like a fuel delivery problem to me. Fuel filter . clogged jets maybe