My Lads Driver has just been to the Mechanics to have a similar issue sorted and his was a multiple issue problem....
1, Fuel filter
2, damaged Coil lead arcing on the rotor
3, dist cap not fitted properly
4, knacked rotor
5, past their best HT leads
6, Carb full of crud and other issues with the dreaded Piersburg which he rebuilt from a spare unit we had...
Might help - might not!!