Fuel Injected BMW
Gravity Feed Auxiliary Fuel Tank Setup
Anyone interested in eliminating the fuel pump and ancillary
wiring from their auxiliary fuel tank setup on BMW K bikes or R1100
bikes listen up.
Parts needed:
| 1 Weatherhead | C5515X6 90 degree bulkhead fitting | $10.05 |
| 1 Weatherhead | C5924X6 Nut | $ 1.18 |
| 1 UTC | P9906-F06 Hose Barb | $ 1.27 |
If you don't already have a valve to turn on and off the flow of
gasoline from the aux to the main you can add:
| 1 Dynaquip | VMH2-A9-1/4 Valve | $5.30 |
| 2 UTC | P9906-F06 Hose Barb | $1.27 |
| 2 Weatherhead | C5205X6 male/male connectors | $1.56 |
These items are available at
Dewald Fluid Power
1023 West Eighth St.
Mishawaka, IN 46544
219-255-4776
Fax 256-0255
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The only other thing you need is an aluminum washer that will fit
over the bulkhead fitting to avoid dissimilar metals problems inside the
tank.
K bikes, remove tank and left fairing knee pad.
Empty gas out, remove fuel pump & filter and flush with water till
tank smells sweet. (no gas fumes remaining) You can skip this step if
you like excitement! Bring Nomex. 
Turn tank upside down and locate the flat plane on the bottom of
the tank between the fuel out fitting and the return fitting.
Locate the exact spot where the bulkhead fitting will reside with
no interference from existing tubes or other items. ( engine for
example) Mark the spot.
Very carefully drill a 9/16 hole at the marked location. The
aluminum is soft and will tear if you get aggressive with the drill
bit, Dick recommends a uni-bit for this procedure as there is less
possibility of tearing.
If you don't know what I mean when I say the metal may tear, get
someone else to drill the hole!
Poke the 90 degree fitting through the hole you have drilled after
backing off the outside nut.
Get the kid or wife with very small hands to add aluminum washer and
secure the nut on the fitting inside the tank, crank it down till it's
flush with the threaded portion of the bulkhead fitting.
Have small handed assistant hold the inside nut with a wrench while
you snug up outside nut on the bulkhead fitting.
Add barb to bulkhead fitting, add fuel hose to barb. No Hose clamp
needed.
Re assemble with plenty of hose hanging off, trim to fit when
location for valve is settled on. Check for leaks.
This is an ideal time to dispose of or alter the cone and flapper
arrangement at the filler if your bikes' tank is so equipped.
R Bikes, the hole should be drilled between the fuel inlet and
outlet ports supplying the fuel injection system ( flat plate )
located on the bottom of the tank as well.
Obviously the aux tank must be located with its outlet higher than
the bottom of the bikes main fuel tank for gravity to work.
Wait for fuel light to come on and turn the valve; takes about 5-8
minutes to complete transfer. Watch for overfill. the fuel level sender
may not be accurately calibrated. If you are getting pressure or a
partial vacuum inside the main tank now ("pfffttt" sound when main fuel
tank is opened) check vent in main tank and rectify. If the main is
pressurized, you may not get complete transfer of fuel.
All the usual disclaimers apply! Think about fireballs and proceed
carefully! Did I mention to check for leaks?
Because there are far fewer moving parts, no gasoline under
pressure, no switches, pumps, and no electricity involved, this method
should be much more reliable and less potentially exciting (think of
fireball again, or riding one) than tapping into the fuel return line,
cheaper too!
Thanks to Dick Fish for supplying the creative "outside the box" idea,
part numbers and a patient and lengthy phone call.
Have Fun,
Larry Cooper
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