If you have signs of Lean AND Rich condition read on

This is for carb model, but may apply to others.

if you have no torque, poor responce from accelerator, and you spark plugs, and tail pipe are black but at the same time you have no hp, then you have a bad spark...

spark should be vibrant (a good crack sound) and strong, most of the time, a defective ignition module is the culprit (the coil gets realy hot and fail after a short period of time) i had this problem and the way i fixed it was chaging the coil and the ignition module, installed a ballast resistor (coil did not have one internaly) and changed all the cables (aso sometimes reason why coil gets hot)

while you are at ti, check distributor, if there is play (doent go back all the way on its own) you have to service it or change it, probably worned out or a spring got loose, that will cause poor drivability

dont under estimate the propper gapping of all the plugs, indexing i havent tryed it but gapping is a must.

at the end, check timing and drive @ 3000 rpm 3rd. gear for 4 min on a flat street, take out your plugs, should be ok, if not, adjust idle mix screw, should be 4 (+/- 1/2) turns out and bleeping the accelerator should give you a crisp, sharp responce. if not and you checked the entire ignition system (grounds, distributor, cables, coil, etc..) and you ARE getting a strong spark (blueish, thick, loud spark) remove carb, service it full you might have a blown power valve (leaking fuel at cruse, you compensate with mix crew and when accelerating or load you feel no responce) or you going fro rich to lean (clogged main) on acceleration