hi im a newby ive had my 85 rangie 7 years now and had no engine trouble at all with her short of the yearley service not touched it. a couple of weeks ago she started running rough backfiring chugging& general lack of power . have checked usual suspects plugs dizzy rotor afm.a couple of days ago it just refused to start.today i have removed plenum cover and the 8 ports are covered in a black tar like gunge. can anybody tell me whats wrong desprate to stop walking trev