The metering rods and springs work in conjunction with the main jet. The main jet allows fuel to enter the carb and is limited on how much fuel it can deliver by the metering rod size. The metering rod is controlled by springs that are different lengths and or strength. The spring's main job is to move the metering rod away from the main jet during different stages of vacuum. If you have a spring that is too soft, then try a slightly stiffer spring or higher vacuum rating to increase fuel during mid throttle. With the FAST O2 sensor reader you can see what the O2 sensor reading is when driving. A lean condition at cruise depending on your engine is anywhere from 15.5-18 air/fuel ratio. I like to tune my engine's air/fuel ratio to run around 14-15 at cruise. You can go slightly leaner, but risk the chance of engine damage if too lean. Wide-open throttle is controlled by the secondary jet and is tuned by replacing the jet; ideally I want my WOT air/fuel ratio to be at 12.5-13.