Project FI Martin
By Stefan Jung and Mike Simon

After partaking in the oppulent breakfast buffet that the Steigenberger Hotel (our home away from home) puts out, we get into the car and take A661 to A5 South to A66 West, which connects the cities of Frankfurt and Wiesbaden. You have guessed it by now: We are in Germany. And on this Saturday in early October, we are out for a specific CBX experience!

After we pass the city of Wiesbaden, we leave A66 a few kilometers before it turns into a two-lane highway, and take the exit for Bundesstrasse B260 or German Federal Highway 260, commonly dubbed “Bäderstrasse”. This loosely translates into “Spa Road” as it connects several towns along the way, all known for their facilities which provide cures for specific ailments through therapies incorporating waters from local springs that contain certain minerals.
We follow the directions that were given to us and soon reach another road that goes off to the left and takes us to an in-the-middle-of-nowhere traffic circle with a strange looking modern monument in the grassy middle. The monument honors a famous son of the town off to the right, Holzhausen. The man is Nikolaus Otto, the inventor of the internal combustion engine, and the monument is supposed to represent elements of a 4-cylinder gasoline engine.

There must indeed be something in the water up there, because we are on our way to the home of another genius in that field who has his residence in the nearby town of Nastätten: Stefan Jung. Known in the “CBX–World” – pun intended – for his awesome alternator modfications, he also got most everybodies attention by putting together a working (!) fuel injected CBX motor. And that in a “Martin” frame with a ton of other chassis and body modifications to boost.

Typical male ego makes me ignore his offer to call him as we enter town so he can pick us up at a meeting point to guide us to his home, and I try to find him on my own. After several laps through the narrow streets of downtown and finally stopping to ask for directions, we arrive at the seemingly correct address. Nothing, at first, indicates that this place is home to die-hard CBX afficionado and I am still unsure until I see the rather unpretentious CBX-sticker on the rear window of a little Renault car parked in the driveway. Rather than ringing the doorbell, I call him now on the cell-phone and in a second he comes walking out from the back of the garage building and welcomes us into the house.We sit down for a cup of coffee (very nice – as it is still in the morning!) and start chatting a little. Expecting a man with several degrees and maybe a PhD in engineering and/or other sciences, I am totally flattened when I find out Stefan is a medical equipment operating, service and maintenance technician and has a welding certificate from a previous career! Talking about hands-on, passionate motorcycle re-engineering. We sit for quite a while and I could have listened for hours to him talking CBX and motorcycles in general, but we came for a purpose and that was his fuel injection bike. So finally, we move to the garage to take a look at it. Again, I am in for a surprise. The garage, while only one car wide, is at least two cars long and shock full of CBXes and parts. The fuel injected Martin CBX that most of you have seen on pictures from the Euro-meeting in Switzerland or in other posts by Stefan himself sits right in front and the owner rolls her out into the daylight, so we can walk around and look at all the details.

Now, let’s listen how Stefan Jung himself describes the evolvement of his project:

“It really all started when I heard that Rainer Hoppe from Wuppertal had built a Moto Martin CBX with fuel injection. Unfortunately, the fuel injection system, which incorporated a controller originally from Australia, never worked quite right. The motorcycle was spending more time on the dynamometer than on the street. As far as I know, the CBX has meanwhile being sold and has been converted back to carburettors.

Around the same time, I had been offered a “Martin”. This specific unit didn’t quite look as one would expect a “Martin” to look - it was done as a chopper, but I was not going to be too picky…
I soon found out, that not only the looks were odd, but the bike also had significant technical problems. During an engine overhaul, the camshaft bearing caps had been installed wrong with the result that the whole engine ended up full of aluminum shavings and was junk except for the transmission.

On a positive note, the chopper builders had not touched the frame itself and it was intact, so all the chopper parts came off. After the engine was removed, all that left was basically the frame and the swingarm. First trials showed that this could indeed be the base for a sportier motorcycle.

A Suzuki upside-down fork and a CBR900 fuel tank looked promising. Also, a “Heru” tailpiece styled after the NSR500 fit nice. This way, the rolling chassis was parked in the corner for the time being.

I could not shake the thought to adapt a fuel injection system to a CBX. It had to be possible with todays technology and tools. Easier said than done! At first, I needed to get information about what was available on the market. I soon decided, that a company abroad would not be a good choice, as sooner or later the support would lack. Especially, since a privateer with too many questions would cause too much work. So I discovered “Trijekt”! A two-person company which procduces fuel injection controllers that are universally programmable with a mapped characteristic. Everything one would need. Only the hardware, like throttle bodies, sensors and injection nozzles had to be obtained elsewhere. I picked Triumph throttle bodies. First impression was good, however, after the adapters had been welded on to facilitate installation to the cylinder head, the throttle bodies were warped . The bodies were deformed so bad that the throttle flaps would not properly close anymore. Too bad. Back to the drawing board…

Finally, I discovered the units from the Kawasaki GPZ1100 DFI. The throttle bodies even fit directly to theCBX intake manifolds, however, out of two 4-piece units, one 6-piece unit had to be manufactured. Very time consuming until everything worked nice and smooth without any lash and play. I was also able to make theTriumph throttle sensor fit.
To find all the other components necessary for a throttle body injection did not pose a major problem. I was able to use the fuel pump and the pressure regulator from other bike models like Honda CX500 TC and Kawasaki GPZ1100 DFI. As air intake temperature is an important parameter required for fuel metering, a sensor had to be adapted to the air filter. Further, the controller requires the exact engine rpm and the crank position to determine the appropiate fuel amount and the correct ignition point. To provide this, a gear was installed into the housing of the ignition pulser. This gear has a notch which sends the data to the controller via an inductive sensor.

Getting the unit to run, however, turned out to be more difficult than I thought. After putting everything together, I was going for the first try. Without any data available - not even talking about a map. Only armed with the laptop connected to the controller and ready to manipulate the ignition time with the “+” and “-“ keys, I hit the starter. The engine fired right up only to to die immediately again after blowing a couple of foot-long flames out of the exhausts. No restart possible. The spark plugs were totally wet and did not provide a spark anymore. A new set was installed for another try. Same thing happens. A reduction in injection time does not yield any better results either.
Great! Almost 2 years of work and then scrapping twelve spark plugs within a few minutes. Something is substantially wrong. As I can’t find a solution, I call the gentlemen from Trijekt, who, as always when I am at a dead end, provide fast and competent help:

“Wrong injection nozzles” is the verdict! It proved to be the right one!

I had only used the fuel mass as a criterion, without considering injection angle or degree of vaporisation. That kind of data is unobtanium anyway and will not be revealed by the vehicle manufacturers. I had picked nozzles from a BMW325i. Unfortunately, these things do hardly vaporize but rather produce a thin beam of fuel. Which is fine in the car, as it will hit the head of the intake valve and is being vaporized there. In a CBX, the fuel just runs into the cylinder. The motor virtually drowns. Through some search, the choice fell on the 4-hole nozzles from the CBR600. These units vaporize the fuel in a very compact envelope. After I obtained 6 units at a used parts dealer – Honda wanted 180 Euro($235.-) per piece – the second attempt was gioing to be much more successful.

The engine started to run stable immediately. Changes in the injection timing were recognizable instantly in the changes of the air fuel ratio and lambda value. Up to 3000 rpm und no load, the characteristic could be mapped easily.
So, the big day of the dyno run came closer. This, of course, is an absolute must for proper tuning. Thanks to a wide-band lambda sensor, the complete map was accomplished within one hour, even including several small breaks.

The lambda sensor was installed right behind the collector and provided a very short reaction time. Storage of the complete map characteristic including additional fine-tuning on the road took only 2-3 hours. The big advantage of the Trijekt controller is, that the connection of a PC allows direct access to all parameters like injection and ignition timing without restriction. In addition, the unit has a “learning” function which provides automatic correction of map values according to pre-selected ? values. In other words: The more you ride, the better it gets. The plug for the PC is conventiently accesible under the seat.



Here is a image of the map. Looks pretty simple, however, especially in the mid-rpm range accuracy is crucial.
So far I have spooled approx 3,000 kilometers without a problem. Including a trip to theEuro CBX Meeeting in Switzerland, right, Monika?

Well, I am sure you will all join me in giving Stefan a hand for this extraordinary effort. A truly remarkable accomplishment. I have seen and heard the bike running myself and I had a really hard time turning down his offer to take it for a short spin. Besides the fuel injection set-up the bike features many other unique details which make this a true masterpiece:

Motogadget combination instrument. Electronic speedo and tach. Tach gets signal directly from engine controller, speedo pick-up is incorporated into  countershaft sprocket.

In order to keep up with the powerplant, front and rear suspension have been upgraded accordingly

Over all it has turned into a pretty nice bike, although it is still a work in progress to some extend. Stefan will probably change little things here and there as he goes along and realizes he can make improvements, but I guess, this is what this is all about. A real "gear head" may never be completely happy with what he has. And through the "rumour mill" we hear, Stefan is considering a Turbo in connection with a fuel injected CBX motor! Can't wait to see this one!