Been down that road on the 110 ECU years ago and I switched to an alternative. A few years ago, Mark Hubelbank started an effort to develop a new ECU for the Viking 110, resulting in the HU708 ECU. I have been flying behind my HU708 ECU for about 5-years now with no issues. Full hardware schematics and software source code are available for anyone to look at and modify. There are some HU708 ECUs and engine wiring harnesses out there, be aware that Jan will blame the non-Viking ECU for any engine or gearbox problems. There is a support group at
https://groups.io/g/HondaFit708huECU that you may want to join. I have a spare HU708 ECU, however I have no plan to sell it. I would be glad to share the engine sensor/wiring diagrams I developed if you are interested.
You mentioned you upgraded the ECU, did you have the engine working with the original red ECU? I have an original red ECU with the last firmware update and some documentation on the original wiring harness that I modified to use with MIL-CIRC connectors on the firewall. As mentioned, SDS is another route you can take for a supportable ECU. Ross has done Honda FIT configurations and seems super helpful.
John Salak
RV-12 N896HS