'68 Barracuda Notch

You said the vacuum needle jumps? Jumps with the lope, or sporadically? And if your timing jumps around with the vacuum signal your vacuum advance must be hooked up to a manifold vacuum source, either that or the mechanical advance starts way too soon. I'm sure someone will correct me if I'm wrong here, but I'm pretty sure advance is supposed to be plugged into a timed vacuum port on the carb so it doesn't do that.