Suzuki Bandit Secondary Butterflies and Oversized Tires | Ask the Geek

Bandit Butterflies
I have a Suzuki Bandit 1250. I've read a lot on many of the forums online where people are removing the secondary butterflies in the throttle bodies for improved performance. Why are these secondary butterflies installed on modern bikes? Is removing this system mechanically safe for the motorcycle? Can I cause myself future damage by doing it?
Peter Kwentus
St Louis, MO

The official word from Suzuki is that its SDTV (Suzuki Dual Throttle Valve) system brings superb response feel, smooth power delivery, improved mileage and reduced emissions. The secondary butterflies do this by opening just enough to provide the optimum intake velocity based on throttle position and rpm rather than letting you decide with your throttle inputs. For example, if you were to open the throttle fully at low rpm on a setup without the secondary butterflies, intake velocity would drop and the engine would not pull cleanly. In addition, the secondary butterflies can smooth the off/on response by opening at a set rateagain, no matter how quickly you open the throttle. And as we’re finding out with more bikes in recent years, in some cases the secondary butterflies are used to restrict the engine’s output to meet emissions requirements. On many race bikes, the secondary butterflies are removed to give the rider more control over the throttle, quicken the throttle response and remove any restrictions. When I raced an SV650 several times, I removed the butterflies on that bike with good results.

You can remove the butterflies from your Bandit, although I wouldn't recommend doing so without some modifications to the fuel system. By removing the butterflies, you will in some cases be effectively opening the throttle more than the ECU believes it to be open, and without a matching increase in fuel your bike could run dangerously lean. Dale Walker of Holeshot Performance (775/463-5394, www.holeshot.com) has seen some impressive results from the Bandit by removing the butterflies and making some additional simple (and relatively inexpensive) modifications, including fuel injection tuning. We're hoping to investigate further if we can get our hands on one of the new GSX1250A models.

Keep those big-tire questions coming
I work at a motorcycle shop in the parts department. It seems like a couple times a week I have guys come in asking for oversized tires for their bikes (SV650s, assorted Harleys, and 600 inline fours). These people are asking for a 200-series rear to put on their 600 supersports, 180-series on a 4.5-inch-rim SV, you get the picture. I refuse to sell these people tires. Their standard reaction is to throw a hissy fit and never come back. The reason I don't sell these tires is because I'm under the impression that this is an unsafe practice. Am I wrong for doing this?
Trace Lindquist
Orion, IL

We're continually amazed at the number of people determined to spoil a sportbike's perfectly good handling by mounting incorrectly sized tires based on cost, style or some perceived performance advantage. In short, it is an unsafe practice and you are not wrong for refusing to sell these people tires. It's one thing to put a wide tire on a custom motorcycle using a matching wide rim and other modifications, but quite another to squeeze a wide tire on a rim it wasn't mean for. Not only does the too-wide tire upset the handling, there can also be clearance issues to the chain or swingarm that can have catastrophic consequences. And I would suspect that a person looking to put that 180 tire on his SV would not be too careful about checking those clearances. The big concern for you is that should one of those purchasers have an accident and the tire be considered even remotely to blame, you and your dealership would be part of any resulting litigation. SR

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