faulty number 3 cylinder tappet and timing.

I now know the cylinder number (3) is the problem. the lifters have all been
changed, the garage also checked underneath (exhaust) the tappet bang is
still there HOWEVER when I advance the timing the banging stops but I can
tell that the car is still running on 7 and 1/2 cylinders.    new plug, new plug
cable, tested from distributer and sparks well in time, what else is there?   If i
disconnect the vacuum line (small pipe) the motor runs faster and marginally
smoother, when I listen to the exhaust I can hear (flut, flut flut sound in time
with the cylinder. so the problem is how do I get the cylinder running smoothly
again, ( one thing the carburetor doesn't tune as it used too, (rich/non-rich,
etc) and when driving the gear change seem sluggish ( it was fine before