I have been trying to track down a vacuum problem on my 68'. I have used the smoke canister method and have been able to locate smoke exiting around the carbs primary throttle shaft (throttle lever side). Its tough to see that area to determine if its exiting just below the shaft at the carb manifold gasket or if its the shaft itself. Does anyone know if the shaft has a bushing or something (exploded diagrams aren't clear) that prevents a vacuum leak or is this an area that doesn't effect vacuum. I have tried applying propane in this area but no change in RPMs was noticed.