I had the same problem, but it was semi-self induced. I did the Waldig shaping on the leading edge of the throttle plate and TB opening. I took the plate off to round it, and when I got it back on, I didn't seat it completely in the center, and created a vacuum leak. Car surged the same way. Once centered, it ran fine.

Bottom line: you have a vacuum leak. Try the propane.
Mike