The ECM.... controls the secondary butterfly plates with a small stepper motor. There is a TPS sensor that gives feedback to the ECM to make sure the secondary throttle plates are where they are supposed to be. You can use TuneBoy to disable this system, and it simply opens the secondary throttle plates and leaves them open while the motor is running. Back in the early days... you simply took the secondary throttle plates out and used them for coasters. You left the shaft and the TPS intact along with the stepper motor so the ECM "thought" the secondary throttle plates were doing their job, and therefore it wouldn't throw a "check engine light". This is what I did and you can feel a difference over stock. You can feel this same difference using the TuneBoy method.
The question I always had was... Why are these secondary throttle plates in there to begin with? I know a magazine writer started all this hoopla about a 7% reduction in power, and I might even be able to find that article (if its still online). I think it has more to do with smoothing out power delivery and possibly increasing torque at certain RPM's (not just down at low RPMs, even Wayne of TuneBoy fame has stated that Triumph Tunes like 20054 have these secondary throttle plates doing their thing at higher RPMs). There may be spots in the power curve where the intake ports will outflow the fuel injection maps... who knows. I don't think that there is an evil plan by "THE MAN" (to keep a brotha down) and steal his 7%.... but what do I know
You mention a "full power tune". This is Triumph terminology that eludes to the fact that some countries like Germany and France have restrictive maps in their ECM's due to local laws. So those two countries have a restricted tune versus a "full power tune", say for the United States. I don't know how Triumph is limiting the power in these cases, but I'll bet that it uses ignition timing and fuel injection along with the secondary throttle plates to do this. In fact... it may not be using the secondary throttle plates at all to achieve a lower horsepower rating, but as I said... I don't know this for a fact...
