The missing battery is likely a bigger deal than you think on this bike. Without it, the regulator has nothing to buffer, so voltage can spike and drop as revs change, and the CDI won't get a stable supply. That alone can cause a weak, erratic spark even if the coil and stator test fine. Get a known-good battery in there first, then clean and check the main earth points at the frame and engine, not just the coil bracket. The ziptie wiring from the previous owner needs tracing properly. Fix the basics before chasing the carb again.
