Yamaha RZ350 “Lab Rat” by Swinndustries

Yamaha RZ350 Custom Cafe Racer

The Lab Rat – a modern two-stroke screamer…

The RZ350 was the final evolution of Yamaha’s two-stroke RD series street bikes — a liquid-cooled, dual-carb street weapon with 60 horsepower on tap, a wild powerband, and a “Perfect 10” rating on the Cycle World fun scale. Looking at the final and most modern street-legal two-stroke you could buy in the United States begs the question:

“What would the Yamaha RZ350 look like if Yamaha were to build it today?”

Enter Daniel Swinney of Swinndustries, a mechanical engineer by trade who grew up rebuilding two-strokes with his old man. Daniel and his father asked this very same question, setting out to build a modern-day Yamaha RZ350, aka the “Lab Rat.” The process would take seven years, with the final stages being completed in Daniel’s cramped apartment garage, but the result is simply staggering — a modern two-stroke street weapon recently showcased at the prestigious 2018 Handbuilt Show in Austin, Texas. Below, we get the full scoop on the build from Daniel himself, as well as a killer deck of shots from Jarred Cox Photography.

Yamaha RZ350 Custom Cafe Racer


The Lab Rat is a one of a kind resto-mod based off a 1984 Yamaha RZ350. The idea was to build a modern day RZ350 with updated suspension and electronics in naked-bike style. The frame has been altered to accept 2005 Yamaha R6 suspension and hide as much of the electronics as possible. The sub frame was completely removed and a new one fabricated in its place to mount a Honda RS125 tail section.

The wiring harness was laid out by hand to integrate the new electronic controls and add in fully programmable CDI and Power Valve units. There is not much left from the original RZ aside from the engine and core section of the frame.

Yamaha RZ350 Custom Cafe Racer
Photo Credit: Handbuilt Show
The Experiment

I grew up rebuilding and riding street bikes with my dad, particularly two-strokes. We built and restored everything from RD350s to Bultacos, an old Steen, motocross bikes, RZ350s, the list goes on. There is something thrilling about the unruly nature of the power band. Sadly, emissions requirements have driven nearly all the street smokers out of the market. The last of the two-stroke street bikes were trapped in the 80’s and mid 90’s, forever frozen in time by the respective technologies of their era.

Yamaha RZ350 Custom Cafe Racer

What would the Yamaha RZ350, one of the latest and most technologically advanced of the two-stroke species look like if Yamaha were to build it today? We have worked to deliver this concept with the Lab Rat – a modern two-stroke screamer and stoplight bandit integrated with modern electronics and suspension, all stitched together with a heavy dose of custom flair.

Yamaha RZ350 Custom Cafe Racer

The Story

The experiment began in 2009. My dad and I took to the lab table in our home shop. With a Yamaha R6 inverted front end and rear suspension and two RZ350 part bikes as donors, we began to hack together a two wheeled Frankenstein. The custom frame was completed in 2010. I was 17 years old and headed to college. The Lab Rat experiment was put on hold in the name of higher education.

Yamaha RZ350 Custom Cafe Racer

Five years and one mechanical engineering degree later, I jumped back in to hammer out the finished product in 2016. While working mandatory overtime hours as a first-year mechanical engineer, the very small amount of free time I had (i.e. sleep) went into the Lab Rat.

As nights working on the Lab Rat became later and sleep was deprived, wilder concepts emerged. Ideas began to flow, and the Lab Rat began to take shape. Two years later, out of my small and cramped apartment garage, life surged through the combustion chambers.

Yamaha RZ350 Custom Cafe Racer

Final Touches

The Lab Rat holds no pedigree. Other than the engine cases themselves and the major suspension components, every part has been engineered and fabricated to fit the build. The devil is in the details, but it’s these small elements that I am most proud of and believe are what sets this bike apart from others. Time and patience were traded for a uniqueness that manifests itself in the finished product. I hope that this project catches the eye of the experienced builder as well as anyone who appreciates creativity and ingenuity.

Yamaha RZ350 Custom Cafe Racer

Frame and Suspension

• 1984 Yamaha RZ350 Frame, split down the middle and widened 41mm in a custom jig to accept 2005 Yamaha R6 Raven swingarm. Maintained original frame centerline and swingarm pivot location
• Yamaha R6 Raven front suspension, triple tree, and disc brakes. Custom order tapered roller bearings in steering head to accept R6 Raven triple tree.
• Custom rear shock hoop and frame structure designed to accept R6 Raven rear swingarm and suspension linkage while maintaining original dynamic action. Extended suspension linkage member
• Truss style subframe designed for integration of Honda RS125 tailpiece. Tailpiece bracket attachment system for additional seat rigidity and ease of tail installation/removal.
• Frame alteration and bracketry for R6 gas tank.
• Hand formed tank accents
• Re-designed and relocated rearset frame mounts
• Right hand side magnetic kickstand.
• Undertail license plate relocation.

Yamaha RZ350 Custom Cafe Racer

Engine, Cooling System, and Driveline

• Original RZ350 case halves and cylinders, walnut blasted and ceramic coated
• Vito’s Performance Crank, trued and welded
• Spec II Stage II porting and port chamfering
• .05 over cylinder boring
• Duncan Racing Powerhead with 22cc compression domes
• Removal of original oil pump mechanism (replaced with block-off plate)
• Removal of mechanical tachometer system (replaced with block-off plate).
• 28mm Mikuni Flat Slide Carburetors
• V-Force 4 Reed Valve System
• Jim Lomas Stainless exhaust system
• Hinson Performance Clutch Kit
• Mattoon Machine R/H engine case with see-thru Lexan Clutch Cover
• Oversized Radiator
• High flow cooling impeller with quick-drain water pump cover
• 25mm offset drive sprocket
• Chariot Performance stator cover with driveline bearing support, offset and retrofitted with
extended output shaft nut for offset drive sprocket

Yamaha RZ350 Custom Cafe Racer


• Re-designed aftermarket stator
• Custom wiring harness assembled with deutsch style waterproof connectors
• Zeeltronic programmable CDI and Powervalve control unit
• KOSO DB02 all in one digital gauge cluster with magnetic speedometer kit and supplemental
water temperature sensor
• Yamaha R6 Raven handlebar controls
• Upgrade to blade style fuse block
• Dual headlight setup, aftermarket tail light and license plate lights
• LED auxiliary lighting
• Hidden battery box and electrical panel
• 3D printed wiring harness capsule

Controls and Brakes

• Custom, made to length clutch and throttle cables
• Venhill stainless steel front and rear brake lines
• CAD designed, CNC fabricated frame adapter plates for Yamaha R6 adjustable rearsets
• Custom shift linkage
• Rizoma front and rear brake reservoirs with clear brake line


• Yamaha R6 Raven gas tank
• Yamaha R6 Raven wheels
• Honda RS125 tail
• Thermo formed kydex seat pan with CAD designed, custom upholstered seat
• Thermo formed kydex undertail cover
• Custom paint job by Mark Seely
• Electrocoated frame paint job
• Powder coating on wheels, headlight assembly, and small components

Yamaha RZ350 Custom Cafe Racer

Special Thanks

Mark Seeley
SuperDave, Done Dirty Customs
Roger Goar
Tony Wilcox
Roy Wang, Creatingway Technologies
Joe Galvan, Top Koat powder coating
Jim Hinshaw, Fast from the Past
Motovation USA
Tin Lizzie Custom Upholstery
Dan, Katrina and Justin Swinney
Rebecca and Gabe Nickens
Gabe and Xavier Villareal
Jarred Cox, J.A. Cox Photography

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  1. Vert impressive build. Good ideas for whenever I get around to doing one of mine. I live in the Detroit area and will not ride on the street anymore. Thinking bout taking one of my 3 RZ’s and doing a drag bike.

  2. Hello I’m trying to get in touch with the guy that built the lad rat can you help

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