Patent Pending: Yamaha XS400 “Roadster”

Yamaha XS400 Custom

Innovative XS400 from Roman Juriš…  

Introduced in 1976, the Yamaha XS400 came during a time when the major manufacturers were foreseeing the end of the two-stroke era and turning their attention to the development of four-stroke street bikes. The middleweight XS was intended more as a reliable workhorse commuter than a sporting machine, competing against machines such as the Kawasaki KZ400, Suzuki GS400, and Honda 400 Hawk.

The air-cooled parallel-twin offered 45 horsepower and the bike turned the quarter-mile in 14.58 seconds, faster than most of the competition and only 0.4 seconds slower than Yamaha’s own two-stroke RD400F. Not bad, but the little 400 four-stroker wouldn’t spur any road racers or canyon riders to wax poetic.

“Neither the fastest in its class, nor the least expensive, nor the most comfortable. It is nevertheless a handsome, functional and economical motorcycle — easy to maintain, miserly with gas, and still competitive in a hotly contested class.” –Cycle, via Motorcycle Classics

Yamaha XS400 Custom

Our friend Roman Juriš of Slovakia, builder of the recent KTM 990 Super Duke we featured, picked up this ’84 XS400 as a non-running donor for an extensive build.

“I wanted a simple roadster, clean lines, slim build, something like the good old 1976 Laverda 750 or 1967 Honda CB250, but in a modern design.”

Yamaha XS400 Custom

Most importantly, Roman wanted to test a new front suspension concept he’s been developing, a Progressive Upside Down Fork (PUSDF) assembly intended to minimize dive under braking — a system he’s in the process of patenting. There are three patent claims:

1. Progressiveness — for example, for a 120 mm suspension travel of the wheel, there is a 60 mm lift in the fork.

2. When springing, the axis of the front wheels is pushed forward and thus eliminates the shortening of the wheelbase.

3. Separation of spring and braking force — the motorcycle does not dive when braking.

Yamaha XS400 Custom

Only the engine and some of the wiring remain from the original donor — Roman built the entire frame from scratch, and the XS is now running a shortened YZF125 swingarm, supermoto wheels, custom bodywork with a lovely speed block livery, and that unique front suspension assembly:

“The front fork is purposefully brand new and protected by a world patent.”

Yamaha XS400 Custom

Roman is waiting for the cold Slovakian weather to clear so he can test the new front suspension system. We can’t wait to hear how it goes!

Yamaha XS400 Cafe Racer: Builder Interview

Yamaha XS400 Custom

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

I’m a hobby motorcycle modifier and I do it for my own pleasure.

Yamaha XS400 Custom

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

Yamaha XS400, year 1984.

Yamaha XS400 Custom

• Why was this bike built?

At the end of 2018, I thought there’d been no new news in motorcycle front suspension for a long time. I had a possible solution, but I knew that I didn’t want to install the new front fork on a regular motorcycle.

Yamaha XS400 Custom

My idea was a roadster with an undermounted engine and a backbone frame. In January 2019, I bought a non-riding Yamaha XS400 and started making a completely new frame and actually everything related to building a motorcycle.

Yamaha XS400 Custom

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

I wanted a simple roadster, clean lines, slim build, something like the good old 1976 Laverda 750 or 1967 Honda CB250, but in a modern design.

• What custom work was done to the bike?

I only used the engine and part of the wiring from the original motorcycle. The frame is completely new.

Yamaha XS400 Custom

The wheels were originally motard, but they have modified hubs and strings. The rear swingarm comes from a Yamaha YZF 125 but is shortened and equipped with a spring unit placed in the style of a Ducati Scrambler.

Yamaha XS400 Custom

The front fork is purposefully brand new and protected by a world patent.

Yamaha XS400 Custom

The whole design was modeled from clay and the parts are made of fiberglass. The paintwork is in the style of Yamaha racing motorcycles from the seventies of the last century.

 

The muffler is under the seat, the on-board instrument is my favorite Koso. The motorcycle is not street legal, but it has all the elements of a homologated vehicle. I wanted to prove that even a bike with rearview mirrors, turn signals, and mudguards can look good.

• Does the bike have a nickname?

It has the name Roadster – it is a tribute to the Jawa 90 Roadster that was produced in Slovakia some time ago. It was a great bike that was ahead of its time.

Yamaha XS400 Custom

• Any idea of horsepower, weight, and/or performance numbers?

The engine is fully stock. (I need to find out the weight.)

Yamaha XS400 Custom

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

The motorcycle is so fresh and the weather in Slovakia so cold that the bike has not yet been tested.

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

Front fork.

Yamaha XS400 Custom

• Is there anyone you’d like to thank?

To my wife, for allowing me to work about 3,000 hours on this project over five years. To all friends who did a great job welding, painting and upholstery. And to those who didn’t close the door when they saw me coming.

Build Process Photos

More Roman Juriš Builds


Event Report: Biker Fest Italy 2024 - International Biker Fest, held each year in the resort town of Lignano Sabbiadoro, is the largest motorcycle rally in Italy and one of the biggest in all of Europe. 2024 marked the 38th annual edition […]
Yamaha XS400 Custom Patent Pending: Yamaha XS400 “Roadster” - Innovative XS400 from Roman Juriš…   Introduced in 1976, the Yamaha XS400 came during a time when the major manufacturers were foreseeing the end of the two-stroke era and turning their attention to the development […]
KTM 990 Super Duke Wildly Addictive: KTM 990 Super Tourer - KTM 990 Super Duke Special from Roman Juriš…   In 2005, the original KTM 990 Super Duke hit the motorcycling world like a two-wheeled bolt of lightning. Here was a naked bike with a chromoly […]
Event Report: Custombike Show 2023 - Custombike Show 2023 from Bad Salzuflen, Germany…  The annual Custombike Show in Bad Salzuflen, Germany is said to be the “world’s largest motorcycle show for rebuilt motorcycles,” typically featuring ~400 custom bikes over a space […]
Event Report: Glemseck 101 - From Leonberg with Love, Drag Races, and Rock…  The Glemseck 101 is the largest motorcycle event in all of Europe. This year, more than 40,000 visitors rode, drove, and flew to the former “Solitude” racetrack […]
Kawasaki ZR-7 Cafe Racer Joy Machine: Kawasaki ZR-7 Cafe Racer - “I decided to build a café racer with knee-down potential.”  Introduced in 1999, the Kawasaki ZR-7 (aka ZR750F) hit the market as an affordable naked bike that harked back to the inline-four UJM machines of […]
Suzuki SV650 Custom Alps Ace: Suzuki SV650 Sport Special - A Sportier SV from Roman Juriš…  Introduced in 1999, the Suzuki SV650 was destined to become one of the most beloved middleweight twins of the modern age. While the bike wasn’t particularly outstanding on paper, […]
Jawa Aprilia Custom Slovakian Supermono: Jawa “JSA 650RR” - Jawa / Suzuki / Aprilia = JSA 650RR… It’s easy to take for granted the opportunities many of us have to own and work on our own motorcycles. Recently we heard from Roman Juriš of […]

15 Comments

  1. Elam Blacktree

    Wow, incredibly well done. I would ride this.

  2. From boring and utterly forgettable to fookin amazing! This has to be one of the all-time great transformations in custom bike building. Well done.

  3. What the factory should have made. Really handsome. I always liked the look of those 80s Yamaha engines. This bike really showcases that pretty little mill!

  4. Decent. i love the red trellis frame.

  5. Wow – that’s absolutely amazing! Looks better than most new factory bikes!

  6. That’s a beautiful machine ! Very fine work.
    I remember seeing a similar suspension set up in the 80’s. There is a photo of it in the book; “The Art and Science of Motorcycle Road Racing”, by Peter Clifford. I believe it was a Honda Endurance Racer. I have always thought the idea of balancing forces against one another was an interesting concept.

  7. Shawn Moynihan

    I loved my 1981 Yamaha XS 400 special! I had so much fun on that bike. I can tell you right now as far as all the custom I have seen this is half down the bike that I want! Everything about it is on and just the fact that it’s got a small engine. Just enough horsepower to have a lot of fun and small enough not to feel intimidated by it!

  8. “YIKES”!!! That be there…one hell of a cool XS400 custom build! One of the nicest I’ve ever seen in that body type. AMAZING WORK! One has to wonder …”What kind of shop…machinery and tool assortment does he have???” This build rocks!

  9. the friends he gets to do the welding? he needs to find a real welder! those birdshit welds are terrifying…

  10. Martin Breakwell

    That`s lovely mate!
    That anti-dive suspension/braking thing does seem to ring a bell from the dim and distant (I think!)

  11. Given the great interest and curiosity around this build, we’ve just updated the article with 40+ build progress photos from Roman. Enjoy!

  12. That Aprilia patent was part of my patent application. I have to find similar solutions to help patent office to be sure about singularity.

  13. Yum yum so sweet, i should try doing something like this from an old GN250 single cylinder engine

Leave a Comment

Your email address will not be published. Required fields are marked *

*