[70DropTop]

Check the vaccum lines coming from the throttle body to the tree on your firewall, if it looks worn/hard replace it. Also check the vaccum caps on the tree, sometimes they will crack and you cant see it as may be on the back, recommend replacing them for a couple of bucks from an auto parts store. The vaccum line going from the tree to the hard tube connector on the modulator could also be the problem, best bet is to replace all rubber parts as they are cheap and doesn't take a lot of time... Where does the carb/throttle vaccum between the firewall and the manifold connect at? Mine was on the carb (Holly) body and I moved it down to the throttle body for more draw... Worked for my 70 Stang vert with 351C/FMX/3.00, but mine had crappy shifting and always wanted to start in 3rd gear when you put it in D. Still havn't replaced the modulator though...