I have a new mechanical and an electric pump. I tested both pumps and they are working great. If I look in the intake manifold it is full of fuel, and when I have the engine running by continually pumping the throttle I can see the fuel coming out of the carbs. It seems like not enough fuel is getting into the engine. I ordered a vacuum guage to test the vacuum. From everything that I have read and researched I have a vacuum leak somewhere.
Not sure if you solved this or not, but I have the same engine (AQ171C, DOHC), a pretty rare (and pricey) one of the red original Volvo's.
First, you should not have (or need) and electrical fuel pump. This engine has a mechanical one built in. I think/fear that an electrical one might be a potential fire danger (in case of a leak).
Second, on the rear most of the two carbs, there's a solenoid valve (connected via a cable harness) that allows the engine to get additional fuel (most likely at cold start - I have never figured out what really controls this valve), and I had similar issue a few years ago. Tore down both carbs to no avail. But as soon as I got this "valve" to function properly again, everything's fine.
It is at least worth trying since you have a great engine when it's running. Small, powerful, lightweight, lean on fuel, but the parts if it does fail are horribly expensive due to the fact that there are not many out there of this engine (compared to the AQ151 and earlier).
Volvo did build a very modern engine (DOHC, electronic ignition, etc) but were likely 5-10 years too early.
If you ever want/need to get rid of this engine, call me, or sell it to someone who auto-cross Volvo's in your area. These engines (never found in any automobile) are very popular due to their high-flow head and can be brought up to 300-400 hp for racing.