El Citron: Kawasaki S3 Two-Stroke Triple by Motobrix

“El Citron? This thing should have been called El Diablo…” 

In 1974, Kawasaki unveiled the S3 Mach II, a 400cc two-stroke street triple with 42 hp and a dry weight of 339 pounds. The bike quickly earned a reputation for smoothness and sweet handling — something the brutish 500cc and 750cc “Widowmakers” couldn’t boast.

“It certainly is spell-binding to skim along just above the ground at the ton and feel like you’re riding on air, with only the rushing wind in your ears to tell you you’re really moving. The two-stroke triple’s smoothness and effortless speed is uncanny…” —Bike magazine, 1974 S3 road test

Our friend Brian Kates of Motobrix, after spending much of his time on modern Kawasaki Ninjas, became interested in owning and modifying one of these Kawasaki triples. After a bit of research, he ended up with a 1974 Kawasaki S3, the donor of bike you see here. Unfortunately, it was in even worse condition than he expected:

“This bike in particular was in pretty rough shape; I didn’t realize how rough it was until I bought it and tried to ride it home.”

He quickly realized that the bike would have to be completely rebuilt to enjoy even in stock form, though that did open the door for more customization:

“I had been dreaming about building a vintage bike with sportbike components, so I decided to start with an engine rebuild, and began gathering parts to build the ultimate two-stroke sportbike.”

At the time, Brian was still fairly new to fabrication (it’s now his actual business through Motobrix and Root 2 Engineering) — so it was an ambitious project, but he managed to retro-fit a rectangular 90s-style box swingarm from a Bandit 600, which required widening the frame but allowed for a 150 section modern rear tire. Of course, there were serious challenges with the fitment, which Brian details below.

The rear shock is from a Suzuki GSX-R1000, and the forks are from a GSX-R600 with matching front wheel.

“The bike essentially became a kind of eBay parts-bin Kawazuki.” –Brian

Brian also rebuilt the engine with a re-balanced crank, 1mm overbore, and Wossner forged pistons. The bike is running a custom oil tank he welded up, a set of modified Higgspeed chambers, handmade subframe and various brackets, and a paint scheme from Black Widow Custom Paint that keeps the previous owner’s yellow scheme intact, if at a much higher quality. The result is a two-stroke super sport that has all the attitude you’d expect from a 400cc member of the Widowmaker family:

“The scream of the Higgspeed exhausts, and the fact that there are three of them, makes it sound like three chainsaws on steroids. It’s frightening; I’ve seen children walking on the sidewalk grimace and hold their ears as I ride by.”

Below, we get the full details on this street smoker and more killers shots from photographer Mark Luciani of Light and Gears.

Kawasaki S3: Builder Interview

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

1974 Kawasaki S3, a 400cc two-stroke triple.

• Why was this bike built?

I originally bought the bike from a friend, after slowly getting more interested in vintage bikes. Most of my riding experience up until that point was on Kawasaki Ninjas of various sizes, but I was excited to get into vintage bikes to do more custom projects.

I honestly didn’t know much about vintage street two-strokes, but I read up a bit on the history of Kawasaki triples and the “widowmaker” nickname, and got pretty excited to own one. This bike in particular was in pretty rough shape; I didn’t realize how rough it was until I bought it, and tried to ride it home. After riding for about a block, the bike stalled and was only running on one cylinder. About five more stalls along the way, blowing dark smoke into the bicycle lane, I finally got home with the bike spewing black oily goo onto my parking space.

I eventually realized that the bike had to be rebuilt for me to truly enjoy it, even if I was going to ride it in stock form. I had been dreaming about building a vintage bike with sportbike components, so I decided to start with an engine rebuild, and began gathering parts to build the ultimate two-stroke sportbike.

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

I wanted to turn the S3 into something modern and sporty while keeping the character of an old two-stroke. Lots of shops have modified vintage 70s bikes with modern forks and swingarms, but I hadn’t seen it done quite like this on a Kawasaki triple before. The concept was influenced by different custom bikes I’ve seen over the years; a kind of mishmash of brat style, cafe racer, and supersport bike styles. Since I was still fairly new to fabrication when I bought the bike, the project was extremely ambitious for me at the time. But I was determined to to do as much of the work as possible myself.

 

• What custom work was done to the bike?

The swingarm was one of the first things I ended up customizing, since it was probably the most difficult part to get right. I envisioned using a simple rectangular 90s-style box swingarm and some research led me to the Suzuki Bandit 600 as having one of the narrowest pivot widths among sportbike swingarms. I chose it also for the look and size of the rear wheel, allowing me to use a 160 width tire. The frame was widened with some plates welded on either side to fit the larger swingarm.

For the monoshock I chose a GSXR1000 rear shock for the look and shape, and fit it to the original Suzuki bandit linkage. For the monoshock mounting points I set the bike up with roughly the right rake for what I wanted and fabricated mounts based on where the shock needed to sit to get the stance just right. I didn’t have a lathe or mill for this project and ended up shaping almost every bracket with a grinder by hand. For the front I decided on GSXR600 forks with a matching front wheel and ordered a steering stem from Cognito Moto to make everything fit. The bike essentially became a kind of eBay parts-bin Kawazuki.

The bike had obviously been through many owners, and the engine was in pretty rough shape. The kickstart lever had been welded to the shaft and many of the bolts were stripped already from previous rebuilds. The crankshaft had to be sent out to Charlie Smith of Triple Cranks in Maryland to get rebuilt and balanced. The cylinders which were badly scored had to be sent out locally to Gord Bush Performance in Toronto to get bored 1mm oversize and fit with a new set of Wossner forged pistons. The oil pump was stripped on all ports and leaking, and had to have all ports helicoiled. The transmission oil drain plug was badly stripped and had to be welded and retapped back to the proper size.

The entire stock subframe was cut and replaced with a sandbent handmade section. For the rear sets, I borrowed from my old SV650 and made up some brackets to weld to the frame. For the two-stroke oil reservoir, I ordered two 4” hemispheres and some 4” steel tube and welded up a mini chopper style oil tank. The battery has been upgraded to a tiny Shorai lithium unit, and sits just under the seat near the tail. With kick only, the battery doesn’t need to be large.

In typical El Citron fashion, the project became a bit of a can of worms:

The swingarm happened to be asymmetrical at the pivot, which meant I had to space the rear wheel more to one side rather than re-welding the frame. After spacing the wheel I had to reweld the brake stay slightly offset, and then had to find a way to prevent the chain from rubbing on the tire. I looked to the supermoto forums for a plan since I knew they usually try to fit fat tires on skinny bikes. I used a 10mm offset sprocket in the front, and a GS500 sprocket carrier to align the chain properly, and then welded a bracket for a nylon chain guard to prevent rubbing. I used a dirt bike slider from a DRZ400 to keep the bottom of the chain from rubbing as well, and had to modify and space the main chain slider from the Bandit 600 off to the side. Even with all these changes I decided to go with a 150 tire instead of a 160 to give a bit more clearance.

I bought a used set of Higgspeed expansion chambers, and had to reweld one of the outer pipes to fit properly with the wider swingarm.

The rear sets sit a bit high because of the position of the exhausts, and as high as they are, the shifter lever was still hitting the exhaust. I cut and welded the lever in a more outward position. The kickstart lever also had to be modified to clear the rear sets, which I did by welding a bent rod in a kind of kickstart lever bypass surgery.

For the headlight I wanted to make something that sits as close to the forks as possible. I noticed that some of the new LED headlights are fairly flat and tried to figure out a way to mount one of them without using the stock off-the-shelf buckets. I ended up creating a minimal system of rings to hold the LED; and sticking to the triple theme, the headlight holder clamps the light in place using three bolts.

I also had to find a place for the choke lever, since I replaced the left switchgear with one from an SV650. I built a perch for the lever to sit on its own just above the headlight and beside the speedometer.

The yellow gas tank was repainted by Amanda from Black Widow Custom Paint (blackwidowcustompaint.com) with a small logo near the front on each side.

• Does the bike have a nickname?

El Citron.

The tank had been painted by the previous owner yellow, with the words “74 SAKI” in black on the sides. The thought of calling the bike “The Lemon” was pretty natural, given how much trouble the bike gave me originally. Instead, with a mix of Spanish and French, the name El Citron just kind of popped in my head, and I went with it.

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

I think it was on one of the first test rides where one of my friends said: “El Citron? This thing should have been called El Diablo.” It’s way more menacing than it looks. The scream of the Higgspeed exhausts, and the fact that there are three of them, makes it sound like three chainsaws on steroids. It’s frightening; I’ve seen children walking on the sidewalk grimace and hold their ears as I ride by. As is probably typical of two-stroke bikes of the era, I would describe the engine response as something similar to a turbo lag. There’s not much power for the low to mid part of the rev range, but as soon as you hit about 6k rpm, the power increases exponentially. It really is the closest thing I’ve experienced to a turbo on a bike.

The handling is definitely much improved from the stock version of the S3. The only thing is that the fork springs and the rear shock are definitely too stiff for the bike. This thing doesn’t weigh much at all, and the suspension components are still oversized for the application. To get the most out of the modifications done to the suspension, I will definitely have to get softer springs. For now it’s a bit like riding a sport hardtail.

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

I’m proud of the overall look of the bike, and I think I was able to truly stick to my guns throughout the process. Sometimes these projects can drag on, and despite it taking three years to complete, I was able to complete the bike as I envisioned it.

Start up and Ride Video

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Photographer, Mark Luciani: lightandgears.com | @lightandgears
Paint by Amanda: Black Widow Custom Paint | @blackwidowcustompaint