I would check the float levels/float saturation/float linkage/needle condition as it might be a carb rich issue. What adjustments have you done? do the boosters drip at idle? As said a lean misfire can kick up the same symptoms as the unburned mixture just goes out the tailpipe where you smell it just like you would smell it if it was excessively rich from a carb issue. regarding a vac leak, how does it run/is there any hesitation anywhere?