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Old 11-01-2012, 03:20 PM   #31346
Lefthand ride Dutchy
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Joined: Jun 2006
Location: Calgary
Oddometer: 2,478
Originally Posted by duanew1 View Post
I believe that the fuel pumps are more of a pressure pump than a flow pump due to the low flow requirements during operation. I would think that the fuel hose is a very large orifice (in comparison to fuel jets) which would not allow pressure to increase to a long shooting stream. A smaller opening would probably shoot farther.

On the other hand, I think that this might be a good way to kick start a stuck pump in the field if needed.
You're one the money. Velocity is a function of orifice and volume. Increase the orifice and the velocity goes down. Not sure if this system uses a pressure regulator, I haven't studied this bike yet. But the pressure achieve in the manual can only be achieved with some back pressure either through an orifice blockage or narrowing or regulator.

On the bm Dakar the fuel pumps are prone to fail when the tank is allowed to run dry often. The fuel is used for cooling the pump. I guess the materials in the pump overheat and expand in different ratios which would/could result in loss of pressure inside pump. This will move the duty point in and area of the pump curve that will exacerbate the situation until failure. I guess letting it cool back down would correct this, but my guess would be that key materials will fatigue early in its design life cycle.

I'm no pump specialist, but dabbled with it a bit. Centrifugal pumps though.
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