Violent jolting at speed

Hello all!

My '84 Mk1 has developed a problem where it sputters and jolts violently at road speed, seeming like the engine is choking itself of fuel.
When I'm parked it idles fine, only operating poorly while the engine is under load.

Bought from a friend who's been tinkering with it for a couple months. We've replaced:
I have menial knowledge working on VWs but this is my first time owning a Golf.
Any advice or guru knowledge would be greatly appreciated!

How's the fuel filler neck, any rusty holes in it?
Shine a torch down it from the filler cap end to check, next have a look inside the fuel tank, there's an inspection hole underneath the back seat and plenty of guides/info on here or web on checking in the tank.

Not sure if your car has a lift pump in the fuel tank as well as a main fuel pump underneath the car, if the lift pump is starting to fail the main pump gets noisy as it struggles to get fuel out of the tank.

How much petrol is in the tank as cars without lift pumps can suffer from fuel starvation if below 1/4 tank if the in tank swirl pot is missing as a lot of after market tanks don't seem to fit proper Gti swirl pots, the original swirl pot has rubber flaps to stop the fuel escaping which over time the rubber rots away then blocks the fuel intake.