For You, Old Fox: Yamaha RD350 Custom

Cus’Tom Motorcycles rebuilds his father’s RD… 

The Yamaha RD350 was one of the great giant-killers of the two-wheeled world, a two-stroke street machine with a race-bred bloodline. In AMA Class C racing, the RD racers regularly blew away machines with twice the displacement, making the 350 a favorite of club riders around the world, and a 70s Yamaha advertisement showed a downtrodden 750 rider at the bar: Don’t feel bad. You’re not the first 750 rider to get blown off by a Yamaha 350.

While the two-stroke parallel-twin made just 39 horsepower in stock trim, it was ripe for modification, spawning a whole cottage industry of tuners and parts makers. What’s more, the RD350 could handle well in the bends, at least for a bike of the period.

“The RD 350 is a cafe racer’s delight with its slim, sleek styling, disc brake on the front wheel and a closely-spaced six-speed transmission… On a favorite stretch of hilly, winding road, you’ll find a race-bred motorcycle in a street machine’s clothing.” –Cycle World, 1973

Our new friend Tom Boissel has been modifying bikes since he a kid racing 50cc machines, and he opened his own workshop Cus’Tom Motorcycle four years ago, located in the countryside near Toulouse, France.

The bike you see here is a 1973 Yamaha RD350, and a very special one at that. Says Tom:

“It was my dad’s motorcycle, with which he came to pick me up from school from time to time. Hence the engraving: pour toi vieux renard (“for you, old fox”). I inherited it after his death six years ago. I hadn’t modified it until then, but I have a little boy who will be 6-years-old, and it will be my turn to make him dream in front of his school — the cause was valid to modify the inheritance!”

The modifications were extensive, including the inverted WP fork, brakes, and wheels from a KTM Duke 390. The swingarm is from the RD350’s legendary successor, the liquid-cooled RD350LC. Here it’s been installed upside-down with a custom Shock Factory mono-shock absorber, along with a rear disc brake and lots of one-off custom hardware to make it all work.

Other highlights include slightly larger pistons, twin 32mm PWK flat-slide carbs, electronic ignition, lightweight rotor, period expansion chambers, a homemade steel tail section with vegetable leather saddle, homemade pegs and foot controls, and much more.

Tom is still breaking in the new top end, but he’s aiming for a truly giant-killing power-to-weight ratio:

“When it’s finished, we will fine-tune the settings, hoping to get 50 hp for 100kg.”

Tom’s RD was a finalist at the 2023 Wheels and Waves “Backyard Project” Custom Contest, and we can’t think of a better tribute to his late father — nor a more exciting ride home from school for his 6-year-old son! These are the stories that make motorcycling so special. Bravo, Tom!

Yamaha RD350 Custom: Builder Interview

• Please tell us a bit about yourself, your history with motorcycles, and your workshop.

I am Tom Boissel, I’m 33-years-old, and my workshop Cus’Tom Motorcycle is in southern France, in the countryside near Toulouse. I started modifying bikes at 12-years-old with my father for 50cc races, and since then I have never stopped.

My workshop has been officially open for four years (www.custommotorcycle.fr). I’m only one; I do all the work (mechanics, welding, milling, lathing, bodywork, frame, paint, etc.) except the seat upholstery cover and the paint for big customer projects. You can find short movies of my work on my Youtube channel. Next up, I’ve started projects number 24 and 25 this summer on two V-Max 1200’s.

 

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

It is a Yamaha 350 RD base from 1973.

• Why was this bike built?

It was my dad’s motorcycle, with which he came to pick me up from school from time to time. Hence the engraving: pour toi vieux renard (“for you, old fox”). I inherited it after his death six years ago. I hadn’t modified it until then, but I have a little boy who will be 6-years-old, and it will be my turn to make him dream in front of his school — the cause was valid to modify the inheritance!

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

I wanted to keep its original line, modernizing it without losing its proportions, keeping a retro side, with a modern touch, leaving it fluid to highlight its mechanics and add a racing side to it, because after all it’s a two-stroke that has the demon of an engine.

• What custom work was done to the bike?

The original parts that I kept are the engine, frame, and tank.

The front axle (rim, caliper, fork, and crown) comes from a KTM 390 Duke; it is the White Power brand, of course integrated by me by adapting the original steering column axis of the motorcycle (see YouTube video below).

The front disc is a racing type (NG brake in 320mm floating diameter). And as a detail, a homemade steering column nut. 

The rear rim also comes from the KTM; it allows you to run a 150 tire to keep the proportions of the bike. To adapt it, it was necessary to change the bearings, redo the internal and external spacers, modify the existing crown holder, and have a custom crown machined.

For the swingarm, it comes from the mythical 350 RDLC, adapted (upside down). It is modified to accommodate the single shock absorber custom-assembled by the French company Shock Factory.

They were kind enough to calculate the most favorable shock possible for me (the lever arm being very important due to the kinematics of the assembly).

The rear caliper is adapted via an aluminum plate type fixing + Cus’Tom stainless steel connecting rod, upside down for the ultimate racing look.

The master cylinder also comes from the KTM (see youtube video on the integration of the rear brake system).

All the selector and brake pedal controls are homemade. The rearsets also come from the mythical 350 RDLC, as do the two period expansion chambers.

The steering damper was recycled from a broken-down washing machine and it is adjustable!

For the engine, all of the intake and exhaust diameters have been slightly increased to fit better with the new mufflers to gain some horsepower in the high revs.

The original Mikuni diameter 28 carburetors have given way to two 32 mm PWKs with flat slides, adapted by custom-made aluminum pipes at the workshop.

The old ignition with contact breakers has been replaced with an electronic ignition with internal rotor, allowing for faster revving (less inertia because the rotor is much smaller) and adjustable ignition advance.

The cylinders have been rebored to accommodate new pistons. The bike is currently running in, when it will be finished, we will fine tune the settings hoping to get 50 hp for 100kg.

The back shell is made of homemade steel.

It houses a trailer taillight, and a saddle in red and gold-stitched vegetable leather that matches the deep candy red of the bodywork and all of the motorcycle’s bronze washers.

The headlight is a standard model, where I added a small fairing to hide the new counter / tachometer / dashboard.

A small homemade front wheel guard coated in matte black discreetly hugs the tire. The tires are Pirelli Super Corsa in SC2 race rubber to perfect the racing look.

Finished Bike Video

Follow the Builder

Website: www.custommotorcycle.fr
Facebook: Cus’Tom Motorcycle
Instagram: @custom_motorcycle_tom_boissel
Youtube: @custommotorcycle8364