I recently installed a Fuel Plus on my 1991 K100RS. Manufactured by Electronic Resources in Oklahoma, Fuel Plus is a fuel computer made only for K-bikes. Fuel Plus replaces the factory clock and, using inputs from the speedometer and Motronic fuel injection system, displays a variety of useful information:
Installing the Fuel Plus requires removing the instrument pod, opening it and replacing the factory clock module with the Fuel Plus unit. You must also make one soldered connection within the instrument pod and another near the Motronic computer under the seat. One wire must be run between the Motronic unit and the instrument pod. Although I had some trepidation about opening the instrument pod and monkeying around inside, I found the instructions to be detailed and explicit. The work inside the instrument pod was actually quite simple.
Removing the instrument pod on the different K models presents different degrees of difficulty. On an RS, the level is probably moderate. The Fuel Plus instructions do a nice job of describing the removal of the electronic windshield on an LT, so owners of the more complex bikes have little to fear.
With the bike on the centerstand, I started by removing both side panels and the clock fuse. I then removed the knee panels that fill the area between the fairing lowers and the tank. I then removed the gauge panels and the trim piece that runs between them. Removing the trim pieces down each side of the windshield allowed me to slip the windshield up and out - I left the little spoiler wing in place at the top.
By turning the bars to one side and then the other, I took the two 10mm nuts and washers out of the instrument pod retainer. I hadn't done this before and wasn't sure how it worked, but I was happy to find that the pod is retained with 'U' shaped clips that fit over two tabs on the bottom. The two threaded portions that secure the clips onto the tab are connected to a flat plate that sits just behind the instrument pod (between the instrument pod and the handlebars). This sounds complicated, but it's far more complex to describe than it is to figure out. It's actually very easy to remove - take off the nuts and washers and slip the flat piece up and out. The instrument pod is now free of the bike, but it won't drop since the clips are still sitting on the tabs thanks to gravity.
You can now grasp the pod and move it free of the tabs, then use a 4mm hex (Allen) wrench to remove the rear connector. As you loosen the rear connector, it gradually pulls free of the pins on the back of the pod.
I took the pod into the house and placed it face down on a towel on the table. Since my wife was out, I used a couple of small glass bowls to hold the hardware as I disassembled the pod. I had never done this before, so I wasn't really sure what I was getting in to. Never fear - the bracket is held to the pod with four socket headed bolts (5mm hex or Allen wrench). Depending on the year, there will be nine or so Phillips head screws that hold the pod shut. Once those are removed, you can gently remove the back of the pod. There is a gasket around the perimeter of the case. Don't worry if you damage the gasket; a new one is supplied with the Fuel Plus.
With the case open, there are six small Phillips screws that secure the instrument package. Remove those and pull the trip odometer reset knob out about 1/4" and you can begin persuading the instrument package to come out. It took a little gentle pulling in a few places, but the unit came out relatively easily. Flipping the instrument package over so that the faces are up, you then use a bent paper clip and some masking tape to temporarily hold the needle on the tach out of your way. You can then remove the clock trim from around the factory clock. This is a little bit of an odd procedure - you need to gently flex the instrument unit towards its back to allow the flanges on the side of the clock trim to clear the instrument faces. Easier to do than it sounds, but a gentle touch is required.
Once the trim has been removed, the clock module can be released - there are four little clips that retain it. The clock comes out, the Fuel Plus unit pops into its place. Make sure that the two pins are properly aligned in the sockets on the Fuel Plus - you can see them from the front when they're properly seated. There's a wire that has to be routed to some pins on the back of the speedometer - make a little hook of the end of the wire around the pin and solder in place. Don't cut the wire, by the way - there's a resistor at the end that is needed.
Drill a 1/16" hole in the back connector close to the brass threaded insert, replace the trim around the Fuel Plus and you're ready to reassemble the pod. Screw the instrument unit back into the case, put on the new gasket, poke the wire through the new hole and put the back cover back on. Make sure you use the correct holes for the instrument retainer screws, by the way. They are adjacent to the case retainer screw holes and it would be easy to make that mistake. Refer to the instructions that showed which screws to remove and you'll be on the right track.
With the instrument pod reassembled, the instructions tell you to place the external wire through one of the square holes on the connector before reattaching the connector to the pod. I found that the external wire was a little on the short side to properly clear the frame when the two sides of the connector were attached. I lengthened the wire coming out of the instrument pod with a short (4") piece of wire soldered on and insulated with a piece of small heat shrinkable tubing, them attached the connector. If I ever need to reopen the instrument pod, I'll need to cut off the connector, but the extension will allow me to do this many times before I need to replace the extension.
The next step is to locate the correct wire in the Motronic harness. You need to unclip the connector from the Motronic, cut the two nylon tie-wraps around the rubber boot and fold it back to see the wires. Mine had another, internal wrapping of some sort of vinyl material that had to be slit a little bit and folded back as well. Be aware that the illustration in the instructions show a connector that looks a lot more like the ABS brain connector than the one for the Motronic on my bike, anyway. The Motronic brain is clearly marked - on a '91 K100RS, it sits flat under the seat on top of the battery. The other computer is vertically mounted between the battery and the front of the rear fender.
The instructions say that the all important wire can be violet/yellow stripe or yellow/gray stripe and that it is a 'larger diameter wire'. I found that mine was of the yellow with gray variety and was buried in the middle of the bundle. You need to access the wire and remove a little bit of the insulation all the way around the wire so you can solder a small wire to it. I made a small hole in the rubber boot, fed the new wire through it, then made the solder connection. I wrapped a tiny piece of electrical tape around the soldered joint, wrapped the whole bundle with more electrical tape to give the new wire some strain relief, then folded the vinyl liner back into place and slid the rubber boot back into position. New tie-wraps on the boot completed the job. I replaced the connector on the Motronic and tie wrapped the new wire to the Motronic harness in a few places.
The new wire needs to run up to the instrument pod, so I included it in some wiring that runs along the frame on the right side of the bike. I didn't remove the tank, but tucked the new wire in next to the rubber air blocks under the tank. The next time the tank is off, I'll tie-wrap the new wire in a few places under the tank. The new wire gets a connector crimped to it, which then plugs into the wire coming out of the instrument pod.
Replace the clock fuse and reinstall the windshield, trim pieces, gauges and knee panels and the job is done. The instructions guide you through some initial settings and you're in business.
A short ride yesterday showed what a valuable tool the Fuel Plus can be. Starting with the default values for a K100, the unit showed a range of about 185 miles as I entered the freeway. As I cruised at about 70, the range gradually increased until it showed something over 200 miles. This resulted from the Fuel Plus learning the actual fuel consumption compared to the distance inputs from the speedometer. As I got off the freeway and started riding some more challenging terrain in a more aggressive manner, the range decreased as my fuel consumption per mile traveled increased.
The Fuel Plus can be custom calibrated to your tank, so adding a larger tank isn't a problem. If you're riding long distances, you can modify your riding style somewhat to decrease fuel consumption (and increase your range) to stretch your riding efficiency and make it to the next source of fuel. This is a remarkable tool for endurance riding and one that gives a BMW K-bike a distinct edge over the other bikes of choice for long distance riders - the Honda ST1100 and Kawasaki Concours. I don't know whether Fuel Plus is available for the K1200RS or the K1200LT, but I don't imagine it will be long before those versions are offered.