So I made a cheap heater blockoff plate a few years back for the Bu, and since the quarters are rusted out I get exhaust fumes in the cabin. Is there a possibilty the carb could be leaned out to avoid this? I know it only pulls about 8"-10" of vacuum at idle, so I'm wondering if I need to change the needles/sests, springs, or both. It's an Edelbrock 1405 (600cfm vac. sec., manual choke, stock as far as I know).