Vacume Spring??

Need advice...
My car won't kick *** from a stand still! This motor "kick *** big time" when in the kids duster but I'm not sure whats-up and why it's sleeping from a "stand still". On the move it digs in pretty good, however I can't even scratch the rear tires...I'm thinking maybe the 4Bs are not opening from a stand still. The car does'nt really bog out...it just granny aways up to speed quick.

Excellent compression 318 with 360 heads, 340 Cam, 600 cfm, dual performer, MSD, ect. The 727 trans was re-built with a TF-2 kit. Rear tires are 8" wide. It also has 3:91 gears.

WHAT I HAVE DONE...
I adjusted the kickdown so it's completely to the rear during WOT. The kickdown can also move forward on it's own will. I think... the carb is set-up correctly, however I'm wondering if I should swap out the vac spring to a lighter one so the 4B open up sooner. That's my guess.
Idea's please...I think..I should be able to get at least a few feet of scratch :cussing: