Exhaust odor, fuel smell or something else from the MGB was giving me a headache, Luckily I got back to the shop and investigated the the trunk area. Ooops, my hand slipped against the gas line... and it snapped from the tank. It must have been leaking fumes and ready to fall apart. A new length of cooper tube was soldered to the salvaged fitting and reattached. Once the line was secured, the car ran fine - no nauseous odor.