oh my god! sum1 else with the same damn problem!!!
its been doing my nut in for ages with my 1.6 Driver.
Ive replaced the Ignition Module, Carb, Coil, and all filters and it still does it, the only thing i think it can be now is either the pre-heater plate in the inlet manifold- this warms the fuel before it goes into the engine, if this does not work then the fuel will chill on heavy acceleration. Then when you slow down the fuel can evaporate?!
Also, it could be the fuel compensating valve, this weakens/richens the fuel when driving, i.e, when on motorway it will automatically weaken the fuel mixture, to compensate the speed and economics. Hence when you slow down it may still be too weak?
Test all your Electrical connections to Carb to see if there is no feed?
Let me know how you get on cause i want to know whats wrong with mine!