Yamaha SR400 Race Bike – BikeBound


Yamaha SR400 Race Bike

Prama Motorworks builds a race-winning {custom}…in simply 4 weeks! 

Launched again in 1978, the Yamaha SR400 would stay in manufacturing all the way in which till 2021, incomes a cult following for its simplicity, ruggedness, and quick-revving character. The air-cooled thumper born from the enduring XT500 enduro, and plenty of riders got here to want the short-stroke SR400 over its longer stroke 500cc siblings.

“In ’78, the bike was a contemporary interpretation of a traditional British 500cc single. At this time, the SR400 is a traditional interpretation of itself, so to talk.” –Cycle World

Enter our new pal Yosef Gumilar of Prama Motorworks, whose first bike was the Yamaha GT80 he bought in 4th grade. At this time, he runs his personal workshop in Bandung, Indonesia.

Yamaha SR400 Race Bike

When the 2023 Motor Adu Basic Bike Race was introduced — the primary circuit racing to return to his space after the pandemic — Yosef jumped on the alternative to race. The problem? He had only one month to construct a race bike!

“I like Japanese muscle bikes, and I questioned if I may construct my SR400 in that type and with different changes and engine modifications to suit my driving type.”

Yamaha SR400 Race Bike

The modifications had been extremely intensive for such a brief construct time. On the suspension entrance, he swapped within the forks, wheels, and swingarm from a Yamaha XJR400, which required appreciable modification, together with shortening the swingarm and relocating rear sock brackets.

Yamaha SR400 Race Bike

He made the fuel tank and fenders from 2mm and 3mm aluminum, respectively, and rebuilt the engine from the crank as much as obtain 500cc displacement by way of longer piston stroke. A BRT Racing CDI allowed for {custom} mapping and a programmable rev limiter, whereas a Keihin 41 carburbetor feats the massive 500cc single engine.

Yamaha SR400 Race Bike

Yosef completed the bike the evening earlier than leaving for the observe! The following morning, he mounted the Triumph Scrambler oil cooler and trailered three hours to the circuit. The following day, he took pole place in two courses (FFA 500-750cc and FFA Japan 500cc up) and gained each races!

Yamaha SR400 Race Bike

Congratulations, Yosef — that’s fairly a feat! Appropriately sufficient, he named the bike “Sangkuriang” after the Sudanese legend of a person who should full an not possible problem of filling an entire valley with water and constructing a ship to sail it in a single evening. With the assistance of heavenly spirits, he dams a river to create Lake Bandung and the overturned boat turns into Mount Tangkuban Parahu, the nice stratovolcano of West Java!

Yamaha SR400 Race Bike

Yosef is duly pleased with what he achieved with this construct, and the way it brings collectively the worlds of racing and {custom} bike constructing in his dwelling nation of Indonesia:

“It’s private for me — in our nation, racing and custom-built bikes are far aside, and I proved to everybody right here that I can construct a {custom} bike that may race on observe. Due to all my workforce on the workshop and to all my pals who trusted in me that I may made it.”

Yamaha SR400 Race Bike

Under, we discuss to Yosef for the total story on the creation of his SR400 race bike.

Yamaha SR400 Race Bike: Builder Interview

Yamaha SR400 Race Bike

• Please inform us a bit about your self, your historical past with bikes, and your workshop.

My title is Yosef.  I’ve liked bikes since I used to be a child. In 4th grade, I bought my GT80, after which in 2013 I opened my very own workshop named Prama Motorworks.

• What’s the make, mannequin, and yr of the donor bike?

I simply know my donor bike is an SR400, however I didn’t know that yr, as a result of I simply bought it separated between engine and body.

Yamaha SR400 Race Bike

• Why was this bike constructed?

I constructed this bike as a result of I like racing. I used to be dreaming sometime I may construct my very own outdated bike right into a {custom} race bike and race on the circuit, after which on March 4-5, the traditional bike race in my hometown returned after a very long time not racing throughout pandemic.

So, after i heard the @motor_adu occasion introduced, I began constructing this bike — I had only one month to construct the bike.

Yamaha SR400 Race Bike

• What was the design idea and what influenced the construct?

I like Japanese muscle bikes, and I questioned if I may construct my SR400 in that type and with different changes and engine modifications to suit my driving type.

Yamaha SR400 Race Bike

• What {custom} work was executed to the bike?

The swingarm I bought is a donor from an XJR400. I needed to lower and weld it as a result of it was too lengthy and extensive for the SR400, and I transfer the bracket for the rear shocks again about 7cm.

Yamaha SR400 Race Bike

The gastank I comprised of 2mm alumunium and the entrance and rear fender comprised of 3mm aluminium.

Engine modification began with the crankshaft; I moved the crankshaft pin about 8mm from 76 stroke to 84 stroke. With a Honda Odyssey piston to cut back engine compression, I bought 500cc and re-ground the camshaft for extra raise and length, however I neglect the raise length and consumption / exhaust valve open and shut levels 🙈

Yamaha SR400 Race Bike

 I used a Keihin 41 carb and a Triumph Scramber oil cooler on the entrance of the bike. I used an XJR400 entrance finish and wheels with Pirelli Diablo Supercorsa tires. Received an SC Mission silencer and Coerce foot pegs, Brembo entrance brake, Protaper handlebar, and Domino clutch lever.

Yamaha SR400 Race Bike

For electrics, I take advantage of a neighborhood model’s programmable CDI referred to as BRT Racing, which allowed me to remap the CDI and put a rev limiter on it.

• Does the bike have a nickname?

Sure! I named it “Sangkuriang” after a fantasy about somebody who builds mountain in a single evening.

Yamaha SR400 Race Bike

• Any concept of weight or energy numbers?

No, I don’t know.

• Are you able to inform us what it’s prefer to experience? How did it do on the observe?

I didn’t have a lot time earlier than the race. I solely completed the bike and had it able to experience the evening earlier than I went to the observe. I simply rode it round my storage that evening. The following morning I mounted the oil cooler, and that afternoon I introduced it to the observe, which is about three hours from my metropolis. However on Saturday, I did QTT (Qualifying Time Trial) and the bike was nice, good energy and dealing with. I bought pole in two courses (FFA 500-750 and FFA Japan 500 up) and completed 1st in each courses!

• Is there something with this construct that you simply’re particularly pleased with? And anybody you’d prefer to thank?

After all, I’m actually pleased with my construct. It’s private for me — in our nation, racing and custom-built bikes are far aside, and I proved to everybody right here that I can construct a {custom} bike that may race on observe. Due to all my workforce on the workshop and to all my pals who trusted in me that I may made it.

Comply with the Builder

Fb: Yosef Gumilar
Instagram: @Pramamotorworks

Photographers: @gianggaw @arianstone_helltrust and @motostylerz