Technical Resources for Fuel-Injected OSSAs

My three OSSAs.  Left to Right: 2014 TR250i (the “A” bike),  2014 TR250i (the “B” bike), 2011 TR280i (fully functional but now the spare parts bike, forks already borrowed for my wife's Electric Motion 5.7)


I bought my first EFI OSSA in the spring of 2014, partly just to study its fuel injection system.  I guess you can say I developed a soft spot in my heart/head for them.  They were (still are?) such cool bikes.  Really ahead of their time, and I do not want to see them relegated to the dustbin of history.  I found it nearly impossible to locate any technical information about them and started keeping a digital notebook of things I had reverse-engineered.  That notebook has morphed into this website (which is best viewed on a wide screen for ease of navigation).  Building the website (a first for me) has been a positive learning experience.  It often forced me to turn cryptic notes into readable prose.

Fixing Things

Kevin Cameron is one of my favorite authors and a constant source of inspiration.  He wrote the following in his October, 2004 TDC column. 

During World War II, a thousand B-29 bombers were deployed to islands in the Pacific.  Assigned to each machine was a crew of 75 maintenance specialists – engine people, sheet metal men, radar techs, etc.  Maintenance proved to be a serious bottleneck.  When General Curtis LeMay took command in 1945, he changed the system.  Among 1,000 engine mechanics, maybe 50 really knew what they were doing, 800 were only procedures trained, and another 150 were useless.  LeMay created separate departments, organized assembly-line style, with service jobs run by the people who knew what they were doing.  The 50 top engine men analyzed problems and decided what needed doing.  The 800 carried out the planned work, while the luckless 150 fetched parts and ran the engine hoists and tractors. Everybody learned something and service became faster and more effective.  The percentage of aircraft available for missions rose significantly.

If you ride trials, like to fix things, and are among the top 5% of fixers, the EFI OSSA seems like a natural choice. 


Although a relative neophyte to trials, I have a lifetime's experience with motorsports and, in particular, the tuning of two-stroke engines. I bought the TR280i partly to study its fuel injection system.

Fuel injection is more difficult to apply to a two-stroke (2T) than a four-stroke (4T) engine.  In 1991, Honda Racing Corporation authored an SAE paper[1] on the development of an electronic fuel injection (EFI) system for a 2T road racer.  Although the paper made it sound like a successful endeavor, Honda never fielded a 2T EFI engine in a single Grand Prix.

The exhaust system (pipe) is the heart of all modern high-output 2Ts.  EFI has been successfully applied to 2T engines that do not use a gearbox (every shift changes the exhaust system's temperature significantly).  Unfortunately, the temperature of the pipe greatly affects a 2T's “delivery ratio” (the amount of air it consumes per revolution).  Variations in delivery ratio make EFI mapping extremely challenging.  A carburetor deals with this more or less automatically as it acts like a crude mechanical mass-flow sensor.

The more highly-tuned a 2T engine is, the more difficulty you will encounter applying EFI.  (Snowmobiles can be very highly tuned, but their CVT mitigates much of the problem.)  One way to think about what highly tuned implies is the width of the engine's powerband and how easy it is to “keep it on the pipe.”  From least difficult to most difficult 2T motorcycle EFI application: Trials, Enduro, Motocross, Road Racing.

1. SAE paper 911224: Development of Programmed Fuel Injection for Two-Stroke Cycle Racer Engine.

My comments on the paper: The system used eight sensor inputs.  The first five are common to 4T Alpha-N EFI systems: engine speed, throttle angle, ambient air temperature, ambient air pressure, and coolant temperature.  Three additional inputs were added for Honda's 2T EFI system: exhaust gas temperature, combustion pressure, and intake manifold pressure.  My impression is that all these parameters are necessary, but still insufficient for a world-class road race engine.

EFI Overview

The TR280i's EFI is an open-loop “Alpha-N” system.  Alpha stands for throttle angle and N stands for number of revolutions per minute.  The base fuel injection map is then modified with corrections for ambient temperature, coolant temperature, and barometric pressure.

The TR280i's system was manufactured by Kokusan Denki Co., Ltd. (KD) in Japan.  KD also made EFI systems for Arctic Cat snowmobiles.  As of January 2016, the company name changed to “MAHLE Electric Drives Japan Corporation.”  Before KD took down the website they called their technology an “integrated ECU.”  Quoting the former website, “This is a proprietary control unit of Kokusan Denki that contains multiple components, such as an engine control unit, voltage regulator, and voltage smoothing capacitor in a single case to achieve compact size and light weight through integration and modularization.”

OSSA History

The slogan “Put a little luck on your side” and the shamrock were integral to the OSSA image. 

O.S.S.A. (Orpheo Sincronic Sociedad Anónima) began operations in 1924 making movie projectors in Spain.  By 1949 OSSA was making small motorcycles, reached its pinnacle in the 1960s, and continued operating until 1982.  In 2010, the OSSA trademark was resurrected by an investment group, and their groundbreaking EFI trials bike was introduced.  Steady improvements were made to the bike until OSSA's untimely demise in 2015.

You will see OSSA and Ossa used interchangeably in the literature.  I do not know which is truly correct, but because the company name was an acronym, I prefer to make it all uppercase.

I do not speak Spanish, but Mr. Google tells me the English translation of O.S.S.A. is Orpheo Sincronic Limited Company.  Given that the company originally built movie projectors, I am guessing Orpheo Sincronic had something to do with synchronizing pictures and sound.

Fun fact: OSSA’s shamrock emblem supposedly represents the escapement mechanism of a movie projector.

Sign outside the factory in Girona, Spain

Production Numbers

Multiple sources indicate that the total worldwide production of all fuel-injected OSSAs was about 1000 units (and that would include the Explorer).  It is believable, but I have no hard data to support that number.  At some point, I would like to create a Registry of VINs and locations.  I have learned a few hard numbers such as 55 bikes were initially transferred when the US importer changed ownership.  There were a total of 22 bikes sold in New Zealand. 

The first two years of production were limited to the TR280i.  In 2013, the TR250i and TR300i were added to the lineup.  I think very few 125s were produced.

Embedded Links (lack of)

I have resisted the temptation to provide links to things outside my control.  Inevitably, those links will become outdated.  Instead, I have tried to provide sufficient information so that you can just conduct a current search for the thing that interests you. 

Additionally, there is a very effective search tool built into the website - just use the magnifying glass at the upper right-hand corner. 


In early 2024 Google Sites changed to no longer allow the preview of Open Office (.odf) spreadsheets.

If you see the message, Couldn't preview file. You may be offline or with limited connectivity. Try downloading instead there is nothing wrong with your system. 

It is still possible to download the spreadsheets.  It may take me a long while to convert all of them into a format suitable for preview.


This website is a work in progress.  It will eventually contain the sum of my knowledge about EFI OSSAs.  If you have information to contribute, you can reach me by sending a private message to user konrad on Trials Central.

This entire website uses Googles Analytics to quantify and improve visitor engagement.