I was spending some quality time with the Rocket III service manual and came across the description for the second throttle stepper motor. In that description it states "The second butterfly optimises engine torque by maintaining intake air flow speed. It does not act as a choke for cold start purposes."
So I started to google search the topic and found that Suzuki uses the same for its bikes to increase torque and smooth throttle response.
The engine incorporates the exclusive Suzuki Dual Throttle Valve (SDTV) digital fuel-injection system. The SDTV system uses a secondary butterfly valve in each 39mm throttle body to control intake area and maintain intake velocity, thereby smoothing power delivery, especially during the off/on throttle transitions encountered exiting a corner.
When the rider turns the twist grip, a cable opens the primary butterfly valve and moves the throttle position sensor.
The secondary butterfly valve is opened and closed by a new type of compact, lightweight DC motor controlled by a 16-bit electronic control module (ECM). The primary butterfly valve determines optimum throttle opening; the ECM reads throttle position and engine rpm then progressively opens the secondary butterfly valve to optimize intake velocity. The results are more seamless and more linear throttle response and increased low-rpm and mid-rpm torque
Upon further reading from other sites much of the same reasons are given however I found on the 2005 GSXR-1000, Suzuki has added a second set of injectors just below the secondaries that spray at higher rpms.
Also found that the Triumph Daytona 600 has secondaries. Jamie I wonder if your 675 does.
The Caviga Raptor 650 also: "It now has a dual throttle valve fuel-injection system with secondary 39mm butterfly valves housed in each throttle body throat to control air intake and maintain air-flow velocity to match power output."
The logical arguement to these claims would be that if they don't limit power then why do they stay open in third, fourth and fifth gears? Well a potential retort is that torque isn't as big of a factor once your rolling at a higher speed, that is where hp matters. Right? So is it possible that the secondaries are in place to deliver more torque in the first couple of gears?
Does Triumph's use of the term "optimize" to mean smooth delivery or highest potential?
I know Tom can attest to the fact he felt more power off the line once they were removed. Anyone dynoed before and after? Are the secondaries just to smooth throttle response at lower RPMs and the other claims just propaganda? Do the secondaries increase velocity and help with fuel atomization? What was the origin of the 7% power limit?
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I know Tom can attest to the fact he felt more power off the line once they were removed
Speaking with Wayne from Tuneboy... He reckons it is a mistake to remove the secondaries. They are there for a number of reasons, NOT just to slow the bike down! Even when they are removed the mapping system thinks they are still there and delivers fuel etc as if they are in place! The fuel mix is different in first and second. I think you are on the right track here Pigman!
__________________ SteveRed
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Secondary Butterfly Questions
Secondary Butterfly Questions 
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