Van is a 1983 1.9 DG.
The engine will start and idle just fine but when I press accelerator the engine kind of wants to stall but doesnt and occasionaly it backfires LOUDLY! The van had been laid up all winter but occasionally started and a few short runs of about 10miles. Then one day it just would not accelerate.
We have checked the electrics; plugs, leads, coil, rotor arm, dizzy and cap all seem to be working fine. The timing has been checked and is fine and no airleak can be identified. Fuel pump and pressure are fine, fuel filter flowing well. Carburettor which had recently been rebuilt (Pierburg 2E3) has been taken apart and seems fine, no blocked jets etc. The garages read outs suggest it is running lean but "dumping a lot of fuel" (not sure what that means). When first started it is possible to rev the negine very briefly i.e. for about 2 seconds before it reverts to idling and will not accelerate again. An oil leak seems to be evident from the cylinder head (Rt side I think). Mechanic plans to investigate cylinder head looking for a failed gasket, valve and so on..is he on the right lines? Is there anything that anyone can think of that we need to look into? I have tried shouting at it but that didn't work

I appreciate any help you can offer.
Best wishes.
Dave.