Jason - I had a problem like this in Chrysler, younger than yours. They provided a factory fix after several thousand complaints. We have all experienced this problem for many years with a lot of cars. the problem is not the carb mounting nor is it the fuel pump. It is the gas supply from the tank to the fuel pump. Apparantly, the fuel pump cannot pump gas vapor; it tends to go to a vapor on the way up to the pump. The factory fix was the addition of a small electric pump installed in the tank and the problem went away. These pumps were made by GM, but are quite simple and still available in many places. Another fix might be to insulate the fuel line from tank to fuel pump. Also, make sure that the fuel tank vent is functioning and its vent line is working. I don't believe your '68 has either of these things on it, but just for the heck of it, make some checks. Hope this might be some help to you.......Bob Harris '81 EFI Imperial