Can you install an O2 sensor and read what the actual fuel ratios are at different rpms? It really shouldn't be that difficult to get reasonable fuel ratios and decent performance. I have to wonder if you don't have an air leak if you can't get it to perform correctly. The manufacturer of the injection has not provided any help ? The thing to do is to start from scratch and systematically verify everything from fuel press at all rpms to timing at all rpms. You might try holding it at the rpm where it misses and use a spray bottle to enrichen the air entering the throttle body with a little fuel. If it dies, it's too rich and if it gets to run better it's too lean. Obviously you want to be outdoors to do this, no propellor, and don't stand directly in front of the throttle body in case it backfires. Then there are all the personal protection devices and a convenient water hose nearby....And proceeding at your own risk. Usually it's done to get an engine to start, but it can also be done just to Guage the effect additional fuel has on an engine. Like any time you are using gasoline, you also have to use a little common sense.