Dream, Build, Race: Kawasaki F5 Bighorn Supermoto

Kawasaki Bighorn 350 Supermoto

Tommy Canellos (@canellos_racing) builds a vintage road-race supermoto…

In 1970, Kawasaki introduced the F5 Bighorn 350, a two-stroke enduro with a rotary disk valve, oil injection, early CDI ignition, and a cast aluminum three-ring piston. Says Classic Jap Cycles:

“The F-5 was touted a ‘do it all motorcycle’ that could be adjusted to suit different terrain and riding styles.”

Kawasaki Bighorn 350 Supermoto

However, it’s safe to assume the 28-hp street-legal enduro, built to compete with Yamaha’s RT360, was never intended as a competitive road racing bike. But when our friend Tommy Canellos (@canellos_racing) decided to move from off-road riding to vintage road racing, he wanted to build a race bike that was special to him and unique:

“I had a rich history with the Bighorn, having fond memories riding one at 12 years old as my regular dirtbike…I romanticized the arm-stretching power that I felt for decades later.”

Kawasaki Bighorn 350 Supermoto

Soon, he’d begun a full-blown road racer project with a vintage supermoto theme, acting as his own rider, mechanic, and sponsor. Developing a new race bike is quite the undertaking — especially with an unorthodox platform — but well worth the many challenges. As Tommy says:

“Life is too short not to race motorcycles…go dream, go build, and go race!”

Below, we let Tommy tell the story in his own words!

 

“Dream, Build, Race” by Thomas Canellos

Motorcycles have always been a huge part of my life. I am fortunate enough to have a large family who enriched my childhood with spectating, riding, and building race bikes. Finally after years of off-road riding I started dreaming about vintage road racing. I knew I had to execute the build of my first road race bike and start making memories.

Kawasaki Bighorn Supermoto

When selecting a vintage road race motorcycle to build, it’s important to determine what era bikes you identify with most. The term “vintage” has now become a large range of motorcycles that include all displacements from the 1990’s and older. I can recall many “vintage” race bikes when they were current and I’m only 31 years old! For me, the late ‘60s and early ‘70s are the pinnacle era for what piques my interest; and just so happened to be what my dad and uncles raced throughout my youth. I decided to build a “period 2, lightweight” racebike, which constitutes an array small displacement bikes by today’s standards. The class includes two-strokes and four-strokes all with various rules in place regulating technology of the era and displacement depending on cylinder count. It didn’t hurt that I would be competing against my dad, uncle and many friends at the track, so bench racing kept my motivation soaring during the build!

Kawasaki Bighorn 350 Supermoto
Tired $200 Bighorn waiting for rescue.

Bike choices were plentiful. The most tried and true bike of the class is the Honda CB350, and if built within specs can be eligible for earlier classes too. The CB350 is a wonderful motorcycle; quick, highly reliable with an incredible parts supply. Kind of like the small block Chevy of the muscle car world. While this would have been a perfect candidate to start my racing endeavor with, I wanted something more unique and special to me. I landed on the 1970 Kawasaki 350 Bighorn as my weapon of choice. For those of you who are familiar with the bike, you may be asking yourself, “Why would you choose an enduro as a starting point for a road race bike?” For starters, good point; but I had a rich history with the Bighorn, having fond memories riding one at 12 years old as my regular dirtbike. I could never start the bike at the time with my scrawny legs, but I romanticized the arm stretching power that I felt for decades later. Although not as powerful as I had recalled, I also had an awareness of Kawasaki’s factory efforts with the Kawasaki Bighorn and the legendary Yvon Duhamel piloting it.

Kawasaki Bighorn Supermoto

While my bike choice may not have been the most simplistic or conventional, I was passionate about the build and the bike was definitely my style. The idea was to build an era correct early 70’s supermoto. I soon purchased a $200 carcass of a motorcycle that would be the platform for the project.

THE BUILD

Bighorn 350 Supermoto

The bike was quickly stripped down to the bare frame, and within an afternoon I had carefully removed any unnecessary tabs and brackets on the bike. The frame was rattle-canned black as I knew there would be plenty of additional welding and adjustments to be made. Steering bearings were upgraded to taper roller, and the stock plastic swing-arm bushings were machined in brass. I spent many months scouring swap meets, salvage yards and classified ads for goodies to complete my vision.

Kawasaki Bighorn Supermoto

Wheels, suspension, and brakes all required a great deal of planning. My class permitted the use of disc brakes so I selected a KZ650 front end with caliper mounts that was beefier than the stock forks. The wheels were salvage-yard MX wheels that were re-anodized. I laced the front rim to a KZ400 hub, mated with a thinned and drilled KZ900 rotor. Finishing off the front brake is a hearty Lockheed racing caliper that was sourced out from a fellow racer. In the process of assembly, all new wheel spacers (internal and external) were machined out of aluminum and where feasible, weight savings measures were taken. The rear brake was left bone stock with the exception of a billet brake stay.

The biggest hurdle of this project was turning a 350cc dirtbike engine into a high-revving road race engine with some more ponies. The Bighorn engine does have good potential with its unique rotary disc valve induction, so I set out to make a reliably fast race bike, which certainly had some teething issues along the way.

THE ENGINE

To start off, the engine port timing was altered. The exhaust port was raised to achieve higher rpm, and the rotary disc was cut for a longer intake duration. The bike was outfitted with a large 38mm carburetor and manifold, which was a sizable increase from the original 30mm unit that formerly hid beneath a cover. The Bighorn came stock with an electronic ignition that provided a straight advance ignition curve. This was typical of two-stroke technology of the 1970s and for leisure riding probably worked just fine. Given today’s technology advancements, a modern ignition was adapted to the engine which provides ignition advance and then retard at high rpms. This greatly helps to reduce engine detonation at sustained high rpm operation.

Kawasaki Bighorn Supermoto

Next it was time to address the low tech twin plug cylinder head. The stock cylinder head provided no “squish band” that all performance two-strokes require. The squish band is a specialized profile of the combustion chamber that centralizes combustion and more importantly prevents pre-ignition. The stock combustion chamber was completely welded, with a central spark plug added. The combustion chamber was then profiled to achieve a more efficient design.

Kawasaki Bighorn Supermoto

Next on the list was the addition of a close ratio gearbox from a similar model Kawasaki F81M. I did not anticipate being able to find, or afford this component but luck was on my side when I came across a NOS transmission at the Vintage Motorcycle Days swap meet in Mid-Ohio. This transmission is virtually identical to stock with the exception of 5th gear. The fifth gear on the Bighorn is an overdrive ratio and makes the bike cruise nicely on the street. (I’ve ridden a Bighorn to Port Dover and was thankful for the overdrive gear at the time!) The last major addition to any great two-stroke power plant is a proper expansion chamber! This complete custom pipe was built by the legendary Gary Braun (@retrodyne). I wanted the pipe to resemble the curling horn of a bighorn sheep and I could not be happier with the performance and craftsmanship. It is truly a work of art. While the pipe was being built I did use an era correct hooker pipe which seemed to work reasonably well despite the drastic dimension differences!

RACING

Bighorn 350 Supermoto

With the racing season fast approaching it seemed as though everything that could go wrong did. Testing the bike unveiled countless quirks and problems that were addressed right up until the night before our first round at Shannonville Motorsports Park. I have learned that no matter how persistent and careful you are with your project, testing and seat time is the only way to flush out weaknesses to your motorcycle. I worked tirelessly to get the bike ready (my wife can attest to this) and went to the track hoping for the best. I was on a new bike, at a new track, and had never road raced before. I was nervous to say the least. Fortunately I had the support of my friends and family and the unbelievable support of the VRRA family.

Kawasaki Bighorn Supermoto
Four days before first race…bike would not shift gears.

After some jetting adjustments following practice I really began to enjoy the motorcycle! It felt reminiscent of winter ice racing… so much so that I had my leg out around the corners still! I had some great battles and knew I was completely hooked. I also received an amazing amount of support and enthusiasm from spectators and fellow racers making the experience unforgettable.

Kawasaki Bighorn Supermoto

As the season progressed, the bike evolved constantly, as did my riding. I managed to attend every race as the bike went through several engines failures, suspension upgrades, gearing adjustments and trackside repairs. I overcame air leaks, melted pistons, crank rebuilds, slipping clutches and the list goes on. Round three at Shannonville was certainly an adventure. After a melted piston caused by an air leak in the carburetor manifold, I made the three hour trek home to pull an engine from an untested barn find bike just to finish the weekend. Maybe that CB350 was a good option after all?… Racing does require major effort on and off the track. It is a big test of your will power when you are the rider, mechanic and sponsor at the same time. Developing a new bike can be tedious, especially when making many changes all at once to a bike.

Kawasaki Bighorn Supermoto
Photo: @spetzo

Reflecting on my first season I am overjoyed with the results. I met some of the most fantastic motorcyclists on the planet, had some great battles and even managed to find myself on the podium. I have also gained an immeasurable bond with the bike, knowing every screw, noise and characteristic… (Even the shriek it makes when engine is seizing at 100mph.) The bike underwent some great R&D and is fairly well sorted at this point.

I was especially proud when the bike withstood three straight punishing days at Mosport wide open. I can’t wait to spend the winter building the “bigger horn”, and see where I can squeeze out some extra ponies. There really is nothing more exhilarating than pushing a home-built 50 year old motorcycle to its limits. Life is too short not to race motorcycles…go dream, go build and go race!!

Builder Interview

• What’s the make, model, and year of the bike?

1970 Kawasaki F5 “Bighorn.”

Bighorn Supermoto

• Why was this bike built?

This bike was built as road racer, with a vintage supermoto theme in mind. The Kawasaki Bighorn holds a special place in my heart because my dad and I rode a pair of them as dirtbikes when I was a kid! I started riding the Bighorn at 12 years old and it’s every bit as exhilarating as it was back then!

Bighorn Supermoto

• What was the design concept and what influenced the build?

I wanted a serious road race engine with the comfortable ergonomics and handling of a supermoto bike. The extra tall dirt track bars make the bike super comfortable and incredible to throw around on the short tracks, not to mention they are just plain cool.

Kawasaki Bighorn Supermoto

• What custom work was done to the bike?
  • KZ650 forks with race tech gold valves and springs
  • Ohlins aluminum body shocks
  • Lockheed racing caliper
  • KZ1000 rotor drilled and thinned on a KZ400 hub
  • 18’’ alloy rims
  • Scitsu tachometer
  • 520 chain conversion
  • Alloy belly pan
  • Aluminum number plates
  • Ported cylinder
  • Modified rotary disc valve
  • 38mm carb replaced the stock 30mm
  • Combustion chamber was welded up and central spark plug/ squish band machined in
  • YZ250 connecting rod
  • Work of art Retrodyne expansion chamber by Gary Braun
  • Close ratio race transmission
  • HPI electronic ignition/ internal style ignition rotor
  • Billet brake stay
  • All aluminum inner and outer wheel spacers
• Does the bike have a nickname?

The bike is lovingly called “the bighorn,” and has gone through many variations over the years.

• Can you tell us what it’s like to ride this bike?

The bike is an absolute blast to ride. It has tons of usable power, handles like it’s on rails, and doesn’t fatigue the rider with the comfortable ergos. I initially had the Bighorn engine in a custom A1 Kawasaki chassis with more traditional road race set up and didn’t enjoy it nearly as much. The bike is super confidence-inspiring in the stock chassis and leans over beautifully. I’ve been told that my dragging air cleaner helps vacuum pebbles off the track lol.

Bighorn Supermoto

• Was there anything done during this build that you are particularly proud of?

I am really pleased at the development of the engine. I went through many engine failures at first until the motor was perfected. Air leaks, detonation etc etc. can plague an old two-stroke. The motor has proven itself now after many punishing full throttle weekends. Bondi Engines played a big part in the success of the engine and the quest for power will continue. We are currently building a “bigger horn” engine for the 2021 race season.

Thanks to:

@bondi.engines
@acceleratedtechnologies (incredible suspension work)
@retrodyne (expansion chamber)

And a special thanks to Richard Biggs for custom machining.

Follow the Builder @canellos_racing

 

 

3 Comments

  1. George Wallace

    What a great story – got me all misty eyed at the history.

  2. I agree! This is more than a bike. It is a story! You deserve all the credit you get for building, riding, re-building. Did you early school reports use words like “committed,” or “never gives up” and “totally loyal?”

  3. Roland Skate

    Didn’t think I’d be interested in reading about a big horn, but Tom and his mates have done a great job. I know the passion and commitment to get something different out on the track and be competitive, so I applaud this one. Well done!

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