I think your problem lies in fuel delivery. Remove lpg mixer and place a shop rag over intake opening. Make sure that all lockwashers and nuts are accounted for and none entered intake. disassemble mixer watching to not destroy gaskets and notating orientation of components. Give all parts a good cleaning. Inspect diaphram for holes/tears if older model mixer. Make sure all orifices are cleared and rotate the lean/reach mixture adjustment full range while spraying cleaner into the inlet. Be sure to clean throttle bore well around butterfly. Do not remove butterfly to shaft screws. Just clean well around it using small brush with cleaner. Use compressed air to blow out after cleaning. Lean/ rich adjustment pointer should be one click left of midway point initially. Idle adjustment will need to be reset. Back out idle air mixture screw till maximum idle rpm is achieved. You should be good to go. That should take care of the "bad" smelling exhaust fumes also.