Yes, your carb is Zenith-Stromberg. Common in Europe, you could also find them in the 120 and 140 models here in North America, with SUs and Webbers being more commonly found in the sport trim and later models as I recall.

The aftermarket and fairly easily found Haynes 240 manual has a whole section on SU and Stromberg carbs, including breakdown, adjustment and fault diagnosis, as well as all the associated stuff like the cold start valve. Everything you need to know should be there. Haynes covers these carbs on the B20A and B21A engines, but it should be extremely similar if not identical to your B19A setup. Idle spec for Strombergs is listed as 850 rpm. SU carb idle spec is 700, although many may find that a bit too low and opt for 750 as I recall I did on my B18 SUs. Idle specs are sometimes a bit different for automatics over manuals, but I don't see mention of that in Haynes. One of the links Kitty and others have given you to the Volvo green manuals will likely turn up the full specs, but without the narrative text sometimes found in Haynes. A lot of the stuff like that on OzVolvo is listed by publication number, not description, so you'll want to spend extra time poking around there and keep in mind these were on 140s as well. I don't have Bentley or Paul Grimshaw's manual, but I'm guessing some excellent stuff can also be found there.

I'm curious. Are you sure your 1981 240 is B19A, not B20A? The B19As are listed as 1974-1978 production in two versions, 97HP (presumably the SU carb'd ones) and a slightly lower compression 90 hp (presumably the Strombergs). I'm not sure why they'd want to give you such an underpowered engine when a bigger carb'd engine was available within the 2 litre tax limit. The Stromberg's also call for high test premium gas -no surprise there.
--
Dave -still with 940's, prev 740/240/140/120 You'd think I'd have learned by now