[Christ]

I read at some point about a DIY solution for small engines that was being called "MicroSquirt"... not sure what ever happened to it.

The problem with controlling an injector by the throttle, is that the throttle isn't necessarily going to match the RPM/Load, hence the reason you should have some sort of flow reference. You can only assume that you have the injector set to run slightly lean, for the RPM that the throttle would normally maintain under a no-load situation (where you'd be setting up the map). As soon as you changed RPM, loaded the engine, etc, or changed throttle, you'd be dynamically changing the fuel curve based on throttle only... while the engine is still loaded or at a different RPM than the throttle can support.

Hopefully, that makes sense to you. You'd still be stuck with a slow responding O2 sensor-backed system that runs worse than a carb'd setup.

I'm trying to be constructive as possible here within my scope of knowledge and thoughts. I don't mean to seem condescending to you, if I'm coming off that way.

Now, if you operated the throttle so that it could only ever be X over 0 (where 0 is "neutral", or the throttle required to maintain RPM under zero load), you could use your latest proposal to build the system effectively, however, RPM changes would be slow and arduous, at best. Sudden changes in load and/or engine speed could cause serious lag problems, and you'd be best to still have an RPM reference so the throttle control could reset itself to 0+X.