Hi!

I see lot of red stars here, but no simple solution. I humbly want to tell you what I used to do with my 1800cc MGB with double SUs, assuming the ones in your Volvo are similar. Everyone told me it (MGB w SUs) was supposed to be a nightmare. Was not. Found an abbreviated workshop manual. Said essentially this:

Take off air filter(s). Adjust linkages so throttle valves open simultaneously. Set idle at 800-1000 rpm. Stop engine. Screw hex nut ("needle" adjust) at bottom of each carb in to full stop. Then, counting exactly, screw out 2 full turns for both carbs. Start engine. Put modest size screwdriver into one intake and lift a few millimeters on carb "cylinder". Engine rpm should increase slightly for a few secs and then drop off. That carb setting is then approx right. Do same with other carb. If, lifting the same amount and with same speed, you get similar response at both carbs, they are set right.

An increase in rpm, when you lift, that stays up indicates too rich fuel. Screw hex nut up 1/6 of a turn, and try again.

A decrease in rpm, when you lift, indicates too lean fuel setting. Adjust hex screw down 1/6 of a turn.

Srewing up and down, and listening, will teach you the trick. Fiddle around with it for an hour or so. Once content, put back air filter(s). Adjust idle rpm screws to desired idle speed. You can, with filters on, adjust richness of mixture by turning screws exactly same amount on both carbs, but don´t be surprised if you get lost and have to take off filters again and have to repeat procedure as above.

Once you learn this you can do it in 5-10 mins, most of the time taken by getting filter(s) off. Later, you will learn to do this every 3 mo or so, to get it just right. Why: Provided you have done all the checkups of ign etc, you should now hear the MGB/Volvo 1800 SU song, if you accelerate at 3500-4500 rpm, with window down.

More to read and with figs at:

http://www.mgb.bc.ca/service/su-tune.html

Points 8 and 9 on that page are essentially same as above and are the ones to start with first. Do the other stuff if those don´t help. The page also contain´s stuff on variants of choke system.

In my experience, these carbs required sparks exactly according to standard specs, for regular driving. So called sports specs spark plugs did not work well. Lots of uneven engine performance.

Good luck!