Back firing intermittent fault ?

Mk1 golf gl 1982 with Webber carburettor
car starts first time, runs perfectly but without warning suddenly starts back firing and cuts out it does restart by stutters until I get up to speed
and then it will cut out and the next set of lights, I'm not much of a mechanic am looking for some advice or help, I have changed the fuel filter,
dizzy cap rotor arm al leads spark plugs but no change, for some reason every time I take the dizzy cap off and put it back on it seems to improve.
does anyone know a mobile mechanic or someone that could have a look at it for me.
Thank you