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.
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
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.