RetroTed

My S1 has an engine issue im hoping someone can help me with
The engine was fully rebuilt 7 years ago and never ran. I purchased the car this year and finished fitting all of the manifolds, turbo, pipework etc and put it into the car,

So the car now starts but its running on at best 3 cylinders and wont idle
Parts replaced
plugs dizzy cap coil leads etc
I can remove the lead off number 4 cylinder and it makes no difference but the cars getting a good spark.
Someone mentioned an injector so I swopped 3 & 4 around and I thought that the misfire had moved across pointing to a faulty injector.
I have replaced it but no difference at all if anything its worse as now as it smells really rich and is chucking out black smoke like its over fueling plus I can remove 3 & 4 leads one at a time and it makes no odds.
Has anyone got any advice, could it be a metering unit or maybe inlet manifold gasket sucking air in
One thing im not sure off but do these cars run an earth strap off the gearbox to the body ? Mine does not have one
Help / advice appreciated

GVK.

To eliminate intake leaks just spray around it with WD40 when its running, if it picks up and runs better, voila.. you're laughing.

Servo pipe is that end of inlet too, have you blocked it off incase servo is leaking? Seen that on RS Turbos 'back in the day'

Have you checked the cam and lifters to make sure they're ok?

Done a compression test?

Back when I had a fringe, my S1 had starting issues and would flood the plugs, metering head cured it. Getting old now though so getting bits must be hard.