Purpose Built Moto builds a two-stroke ripper…
The Yamaha DT400 is one of our favorite two-stroke enduros of the 1970s — a wolf in wolf’s clothing and a howling fury to ride. The factory bike may have dynoed at 24 horsepower and 24 lb-ft of torque, but it always felt like more than that, with the front wheel lightening with every touch of the powerband.
What’s more, we can say from personal experience that it’s a bike that makes you feel like you’re getting away with something illegal just by riding it on the street. It feels like riding a motocrosser with lights.
Recently, we spoke to Tom John of Australia’s Purpose Built Moto, who’s had a similar experience with this ’75 DT400. As Tom says, the bikes were light for the time, had some of the nicest tanks of the 1970s, and they had that ripping 400cc two-stroke at heart:
“Now I won’t lie to you and say it’s a darling to ride, it’s an animal, a snarling twitchy fucking animal. If you’re looking for a bike to take a leisurely cruise around town, this isn’t what you want. However, if you want a bike that doesn’t feel happy unless you’re ringing its neck, it can get around on the street but will be at home down a fire trail, and no matter where you point it will deliver a heap of fun.”
Recently Tom and the PBM crew decided to re-imagine this 1978 Yamaha DT400. These bikes went from twin-shock to rear monoshock suspension in ’77, which was quite a performance upgrade, and Tom and his crew saw the potential to take this model to the next level:
“In stock form they’re an overpowered farm bike, a vintage enduro racer you can register, and that bike your drunk uncle told you to have a go on at a family BBQ when you were 10 and it scared the life out of you. But when you take them down to the bones, and rid the chassis of its tired and slouching suspension, the DT400’s look more like a bike you could point at an MX track. This is what our Rider Clint was after.”
To start, they stripped the donor bike down to the bare frame, heaving out the busted fenders and blown suspension.
“I wanted to create a very classic VMX look, but with modern MX bike sensibilities. Walking the line between the two.”
They sourced the front end from a 2014 KX250F, and Costanzo Racing Tuned set up the front and rear suspension to match. A set of 21″ / 18″ Excel rims were laced up, using the KX250F front hub and the stock hub out back, and a set of Dunlop D606 dual-sport tires were spooned on.
Hey, you might ask, aren’t KX250 forks gold? Says Tom:
“You’ll notice the smoky silver finish on the forks. The standard KX250 straw gold wasn’t going to work here, so before the forks were sent for tuning we stripped the tubes in the lathe and semi-polished them with a very fine sandpaper before having them clear anodised. A small touch, but it’s the details that count right?”
They went on to rebuild the engine with a 12V Vape ignition and a new Mikuni carb. Then it was time for the real work to begin: fabrication. Tom found a DNA air filter designed for a BMW R18 that fit the bill:
“So I set Dylan to work fabricating an airbox that would have the panel filter fastened to the outside, stopping any debris off the open wheel from entering our intake. On the opposite side is a handmade oil tank that’s plumbed into the onboard oil pump.”
Tom says he recently tooled up for sheet-metal shaping, and this is one of their first bikes he had a go on, shaping up a set of custom aluminum fenders, fork shrouds, headlight surround, and more.
“In our projects to come this year you’ll see a lot more hand made aluminium body work as we sharpen up those skills.”
The cockpit is decked out with ProTaper bars, Domino throttle, PBM push button switches, PBM Scrambler mirrors, and aftermarket levers.
The dash is an all in one digital cockpit, the Daytona Deva — very trick!
They wanted to retain the stock power delivery, so they sent out the original expansion chamber to be refurbished, fitting it out with an FMF silencer modified from a KTM 300EXC. The entire exhaust was ceramic coated.
They made a fiberglass seat pan and small electrics tray to house the brain of the lighting system, a PBM Black Box module — much similar than an M-unit, says Tom — along with a small battery to allow the use of LED lighting on the new 12V system.
Timeless Auto Trim shaped up a black gripper seat with red details.
The rest of the bike was done up in a scheme that harks back to the iconic Yamaha white, red, and black livery. Says Tom:
“My personal favourite is the headlight plate colour design, something about it just gets me excited to ride. These crisp colours have been laid down by none other than Justin at Popbang Paint.”
The result is a DT400 scrambler / restomod that manages to mix VMX nostalgia and modern amenities into a single machine that we’d absolutely love to own.