The backstory (bear with me):

Bought a '69 144 for 500$ off these girls, rushed into it and quickly realized it needed a bit of work and transformed from not really even knowing what a sedan was to rebuilding blower motors and carbies, replacing tie rod ends and repairing all the lights etc. (I'm freshly 18 by the way and a huge vintage volvo fan)

Fixed the car up and got it registered by myself, rebuilt and tuned the SU HIF-6 carb I had on it, it was running awesome (though I had always had a little bit of trouble with it bogging down and idling low in drive).

I then proceeded to drive it 1300km to byron bay at the top of NSW and back, the drive was really awesome and fun. I did however realize halfway through along the highway that I had some sort of oil leak issue, as I had ran it dry and could hear the rattle of the tappets (sorry).

During the journey there and back, I did notice I had to continually adjust the SU idle mixture a little leaner each time, and by the time I got it home the jet was really high in the throat (visible). 2 days after getting back, the car was spewing black smoke (unburnt fuel) from the exhaust, idling like *** (couldn't even drive it down the street) and that was with the carb tuned all the way lean, and you definitely couldn't start it richer than that.

Showed my dad and he said something was definitely up, after some digging we realized we had a cracked intake manifold and some previous owner had just used some araldite to weld it back together and the heat from the drive had pushed the split (haha *** how did I even get back).

From there after welding, replacing and getting nowhere, long story short a volvo enthusiast in town did me a huge favour and gave me a new intake gasket, intake manifold and a dellorto carburetor to match, it was one he had on a 144 once himself, but it had been sitting under a shelf for years.

I put it all on, and we had it running awesome without adjusting the tune or anything - perfect tickover, so my dad and I built a whole new custom throttle linkage and it works awesome except after finishing that we tuned it and the exact same problems came up!! I was devastated I was sure it was either the SU or the intake manifold. Though bear in mind for a little while the dellorto was giving great power and clear exhaust (and we hadn't tuned it from the way it was tuned for the last 140)

SO that brings us to now.


Symptoms:
Running rich no matter what we do, black smoke exhaust, sooty plugs, rough idle that bogs down in drive really fast and barely driveable. Have to hold it above 2500~rpms just so it doesn't choke. We tuned the carby to the exact manual specifications, did heaps of research into the carb etc.

When the SU carb was on it, the air piston wasn't getting an even ratio of lift to the throttle which made me think there was a vacuum leak screwing up the carby low pressure environment it needs

Additional info:
B20A engine
Single carburetted 144 1969
Compression on all cylinders (cylinder 2 is a little bit lower but still above 125 psi at least)
Timing is right on 12 advanced and there is clearance on the contact points, also getting spark to each plug [EDIT: 1st cylinder has dodgey spark]
Valve clearance is right, no burnt exhaust valves
I cleaned out the crankcase and tappet cover breathers

the brake vacuum assist valve works one way only as it should HOWEVER when the engine is running an audible 'clicking' noise is coming from the brake vac. assist/cylinder? though i've had it running well with same noise

HELP needed, please all advice is appreciated

my ideas: possible vac leak that isn't obvious, or running the carby for a bit dislodged some gunk and blocked a jet or something like that or maybe some electrical issue.