No power under accelartion

[grumble]

Had our 1975 T2 for a while now, and since May, it has not been driving great. 
1. Started reving really high in idle once been driving for a while to the point of having to stop, seemed to get better on its own accord but just comes and goes now.
2. Been driving very sluggish for a while, will sit at 80 but struggles to get there, and surges(think that's the best term) through the gears if foot not right down. Struggling with hills more and more.
3. Today will not drive off unless pumping the accelerator. Cuts out with normal pressure on the accelerator. Starts first time and will idle OK(although a bit rough)  Took it for a drive and completely died on a uphill. Managed to get it started to turn around to head home, but even on the flat in first gear no acceleration. Also when accelerating it is back firing a bit.
New spark plugs and cables fuel filter etc fitted a few months back.
Checked all pipes and connected apart from the vacuum hose of the distributor which a few people have not been able to find a home for it. Normal place has been capped off.
Just looking for any ideas as i am at a lost, hope the above makes sense.

I assume that it is a type 4  engine, a good starting point would be check the balance tube elbows on the manifolds, fuel feed and pressure,float levels in the carburettors, check the accelerator pump discharge. Check the valve clearances, dwell angle and timing, adjust the idle mixture and speed, balance the carburettors with a synchro syn. Refit the vacuum advance tube , some of these run to the R/H carburettor but most run to the L/H carburettor. Carry out the above with a vacuum gauge connected to the balance tube (this also makes it easier when the idle mixture being adjusted.)