planesmistaken

i have a 1985 escort 1100 mk3, its been running fine after recently replacing a contact breaker, but recently it won't idle at all. i only seem to really get problems when i fill up with unleaded fuel. the plugs are 12 months old.

does anyone know whether this could be a fuel or carburettor problem? this car would have been designed to run on leaded four star fuel, which is no longer available. this means that the lack of lead in the fuel would mean the valves could burn. does anyone who runs a similar age car know whether it would be worth using a lead substitute fuel because of the octanes or whether a carburettor replacement or overhaul would be necessary?

please reply if you think you can help. i'm not a mechanic so this confuses me quite a bit, and i'd rather know what the problem is before i start throwing money at it.

thanks,
adrian.