Are you in Australia? From the way you describe your Volvo, it is carburated. My best manual, the Bentley is for US models, no carbs. I have an old Haynes manual, 1974 through 1980, which covers carbs. You might look around for one of those. As far as the sucking sound from your carb, they do make this sound when the air cleaner is off. It's normal. If you hear a hiss, it is probably a vacuum connection missing and the car will run lean. As far as the carbs on Volvos, I can't help you. The Haynes lists them as SU or Zenith-Stromberg neither of which I have worked on. Good luck on finding a manual, they must be around somewhere there.