golf mk1 gti engine misfire

hi im new to the club and wondered if anyone could help me im am getting a misfire on my golf mk1 gti its happening between 1000 and 1800 rpm its like a flat spot but after you get over that it pulls like a steam train ive changed the plugs cap rotar arm leads plugs air and fuel filter but its still doing the same its driving me nuts now any help would be great thanks