TE449 Dual Throttle Shaft Operation in Slow-mo

[Dangermouse449]

Hi all.

I promised a while ago to make a video of the throttle shaft actions of the Kehin/BMW Double Flap system. I strapped on my Sony Action cam & ran it at 120fps slow-mo.
(This is a real-world test, not a dyno run)

In the video, you can see several times where the second flap heads to the 'closed' portion of its range while the main throttle is opening. It does this first early in the vid, right off idle at light throttle, this is one of the things that brought about stalling/flameouts on my bike!
This was my reasoning for removing the second plate from the shaft.

With everything slowed down, you can also see the designed in delay of the second shaft stopping the normal 450cc hit from occurring.

Keep in mind that the two shafts work in the same direction to open.

View: https://www.youtube.com/watch?v=7Vn_9JxDOz8

 

[Tinken]

The second butterfly is doing exactly what Keihin engineers designed and intended it to do. Eliminate "throttle snatch", the quick jerky throttle response evident in modern fuel injected motorcycle engines. By reducing this, the secondary butterfly improves the over-responsive power characteristics of a standard single butterfly system. The stalling is caused from an interrupted signal from the ecu to the stepper motor, most likely from the poor cable harnesses placed on 2011-12 449 and 511s. Husqvarna was aware of this issue and replaced these harnesses mid 2012-14. The upside to removing the butterfly also removes the chance of stalling, while the down side is the reintroduction of throttle snatch to a motorcycle which once had an electrically smooth power band.

 

[Dangermouse449]

It is a shame that Husqvarna didn't choose to repair the earlier bikes under warranty if there was known cause of a fault (Potentially dangerous on-road)

While I really don't want to start an argument session, I will state, that the TE449 is not 'snatchy' at all without the second butterfly installed.

I understand what you mean, but it is perfectly controllable at light throttle openings to the point of being able to be ridden trials-bike style though rough terrain. I'm a relatively old guy with only average fitness, I can still pop up small rock faces & jump logs with being overwhelmed by the engine.

The 'smoothness' of the delayed second throttle does certainly make the power curve flat.
Fine for on-road use but makes it difficult to perform basic things like pulling a wheel-stand in a tall gear to clear puddles etc.

As a mechanic with EFI experience, watching that second butterfly close while the main throttle is being opened makes no sense whatsoever,
regardless of the fact that it is working as intended.