I've messed with mechanical injection on alcolhol sprint cars, drag bikes, and a blown outboard.
Pretty simple stuff. You just put different size pills in the return line to restrict it and richen it up. Bigger pills to lean it out. You can also mess with injector sizes and pump drive ratios.
Gas is more finicky than alcohol, but the principle is the same. Most setups have hi and low speed pills (determined by the fuel valve) but I hear there are three stage ones also.