The main variables for determining how much fuel to inject is engine load and RPM as these are the best indicators of air flow. There are other "trims" like engine and air temp, barometric pressure, accel and decel, etc, but those two are the big ones. RPM is easy to determine as it's a direct measurement. Load is more difficult and must be measured indirectly, however, there are several common ways its done. The most simple way is by measuring throttle position via a TPS (angle, closed to full or 0 to 90 degrees) the greater the angle the higher the airflow, but its probably the most inaccurate. Another way is to measure the pressure (vacuum) in the intake manifold via a MAP sensor (manifold absolute pressure). The greater the vacuum (such as at idle) the lower the air flow rate. The final common way is via a "hot wire" in the throttle body which changes resistance (temp) in response to airflow. The problem with the later two is that it's difficult to get a steady signal on a single cylinder engine due to pulsations in the intake tract. So the simplicity of the TPS sensor outweighs its accuracy issues in this case. Given a TPS/RPM based OPEN LOOP system, a simple table is created with TP on the Y axis and RPM on the X axis. a typical table (or map) will have 100 cells or so (combination of rows/columns). The engine is then run on the dyno and held under load at each "cell" at which point the engineer will input a number corresponding to the amount of fuel required to meet his desired air/fuel ratio which is being measured in real time. Once all the cells in the table are input and all the points connected through interpolation you have your fuel map. Of course, the test conditions are typically pretty ideal and the system needs to be able to compensate a bit + or -, that's the purpose of all the various other fuel trim sensors. On a Closed Loop system a slightly different map is generated where the desired AFR is logged in each cell instead of injector on time. The wide band O2 sensor continuously monitors the actual AFR (Air Fuel Ratio) and compares it to the desired AFR and using various algorithms adjusts the injector on time until the two match. This happens very quickly and requires a very fast processor in the ECU, therefore, in some early systems closed loop operation is halted in favor of open loop under conditions of heavy load and/or high rpm. Closed loop was originally designed to lower emissions at idle and low load conditions. My 09TE450 originally operated under both open and closed loop depending on the operating conditions. Most people like me have added the "Power Up" components which effectively eliminate the closed loop system in favor of the one or two base maps (open loop). This puts more emphasis on proper tuning, particularly at lower throttle angles, since there is no feedback system. In addition, according to the manual my bike has a MAP sensor as well as a TPS. I'm not 100% sure, but I think the MAP sensor acts as another trim sensor, cutting fuel under heavy compression braking for emissions purposes. So back to the original open loop fuel table and the TPS. On my bike you can only tell the ecu that the throttle is closed (idle) by using the IBeat software. The sensor itself is a simple linier potentiometer and the factory has already determined that the resistance changes X ohms for every degree it is rotated (lets say 1 ohm per degree to make it easy). So ideally given a "closed/idle" point of 1 ohm the addition of 30 ohms means the throttle is now at 30 degrees (33%) open. The ECU simply looks at fuel table for the cell that corresponds to the current RPM and 33% throttle and uses the value in that cell to command the injector open time (plus/minus any trims). Here's where the confusion come in. The factory sets the closed throttle angle using the throttle stop screw to maintain a specific idle speed/emissions. There's a small air bypass screw as well, but in my experience it has more influence on the actual AFR than RPM. So, if one adjusts the throttle stop in a way which closes the throttle slightly more then the "factory" setting and then "resets" the zero/closed throttle position using IBeat, the number of degrees to physically open the throttle to full just increased by this small amount. Remember, on this system the FULL OPEN position cant be reset, so the ECU simply adds the extra 2 or 3 degrees (in this case 2 or 3 ohms) to the total number of ohms which is now 92 or 93 ohms or 102 or 103% throttle. That's why many people suggest adjusting the stop until a specific full throttle reading is obtained on IBeat. The opposite is also true. And as mentioned in my original post, a few degrees can make a huge difference at smaller throttle openings as the ECU is now looking up a fuel cell (along with RPM) with a value considerably different than the intended (factory) cell at the physically identical throttle/RPM position.
