You don't need the harness unless you are adding FI. What do you mean by putting out? Start with the basics. Fuel delivery, ignition, and exhaust. Yes, exhaust. A clogged cat or muffler will hurt performance. Check carb settings. Check timing. Is timing constant above idle? If timing jumps around, bigger problems exist. Do you have a vacuum guage? Connect one to the carb. Read this to interpret vacuum readings:
http://www.centuryperformance.com/fo...a-Vacuum-Gauge
A vacuum guage is $15 at Harbor Freight. It's one my most trusted tools in my garage!