Car -ae86

motor / part in question - 20v 4age and running gear

problem - the situation is that i have recently installed a silvertop 20v into my ae86, its running trumpets, an adaptronic ecu and individual COP's, the car has not been fully tunned but the tuners have fiddled with it a little to get it running decent for now, it has been running pretty nicely and ive had no troubles since they did this a month or so ago, but then almost two weeks ago i was driving the car and it started missfiring slightly, more under load (accel & hills) i thought it may have been fuel surges as the tank wasnt very full, then later that day on my way home she died and would not re-start and we towed her home, i thought it was just out of petrol, but once i had re-filled the tank the car still would not run properly, spluttering at first only whilst being driven and under load again, but slowly getting worse, i have checked the plugs, they are fine, ive put a few different sets in (one brand new) and none of these have cured the problem, the car now finds it hard to start and will barely idle on its own, it seems to be running quite rich (probably due to the lack of a proper tune) as there is lots of black smoke from the exhaust, it will rev but as you do this it will splutter and lose power randomly, i have checked all the fuel pump and filter at the tank and they both seem to be working fine which again is backed up by the fact that it is running rich.

occurs/started when (if applicable)- almsot two weeks ago.