A shiver ran down my spine at the first sight of this motorcycle, the memory of a freighting experience brought back to life by just two letters, DT. Then listening to builder Tom Gilroy recall his early encounters with the same bike let me know I wasn’t alone. AG/Farm bikes are a big thing in Australia and for many of us a ride on an uncle’s two-stroke on the farm was our first experience on two-wheels, normally they’re a small capacity machine, but if they happened to have a DT400 then you popped your cherry with one almighty scary scream. Now for one very lucky customer of Purpose Built Moto, Tom has taken that adrenaline filled power plant and given this 1978 Yamaha DT400 the full custom make-over that it’s always deserved.
At ten years old I gently twisted the throttle on a dull looking DT as I exited a paddock gate and turned onto a small dirt farm track. I pinned the throttle, and the front wheel was instantly and violently in the air, the world was spinning, the bike was screaming and I crashed badly to the ground. I was alive and I was hooked! Tom recalls similar scary memories of the overpowered farm bike and now even owns one himself, “But when you take them down to the bones and rid the chassis of its tired and slouching suspension. The DT400s look more like a bike you could point at an MX track. This is what our rider Clint was after.”
With the busted fenders and old suspension pulled from the machine, Tom could get down to work turning the chassis into a roller. “A 2014 KX250F front end was sourced, including the front wheel and brakes. Grafting this onto the front end and lowering it a touch set the height for our rear suspension that was sent out to be lifted to suit. Costanzo Racing Tuned set the chassis straight once again.” The front suspension has been tuned and the fork legs thrown on the lathe to remove the gold finished, semi polished and then given a clear anodising.
The KX hub is used at the front with the stock unit remaining at the rear, both are laced to black Excel rims, measuring 21in up front and 18in out back, wrapped in Dunlop D606 dual sport rubber. That angry engine was next, and it has been pulled down and overhauled, and a new Mikuni carb fitted up. Electrics have come a hell of a long way over the last few decades and a 12V Vape ignition system ensures the bike has the best! On the exhaust side of things, you’d usually see an aftermarket expansion chamber fitted up, but with the stock unit doing such a good job at providing smooth power delivery, Tom opted to repair the original, ceramic coat it and fit a modified FMF muffler.
Wanting to retain an airbox, “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.” Time for the looks to get an update and Tom wanted to mix the best of VMX classic styling with modern MX usability. “I’ve recently tooled up for sheet metal shaping and started fabricating our own custom aluminium fenders,” Tom tells us, and boy is he off to a flying start.
The rear fender is affixed via a custom set of mounts worked into the frame and the OEM level of fit and finish results in an ultra-clean look. “The front end is also dripped out with custom aluminium work. Fork shrouds, headlight plate, and front fender all handmade parts. Taking a lead from the rear fender, the front was made to suit and complimented with a headlight plate that’s a real stand out piece on this bike.” It’s then all been dressed up with a 4.5in Purpose Built Moto LED headlight and a pair of running lights at the bottom of the plate.
This begins the electrical transformation of the machine and it’s all centred around Purpose Built Moto’s own Black Box module, which is paired with a small lightweight battery. “The black box module can get hidden just about anywhere and takes care of all the functions you need when using slim push button switches.”
The rear of the bike utilises a 3 in 1 Hollowtip LED piece, which is brake, taillight and turn signals in one and a Daytona Deva digital dash brings the instrumentation into the 21st century. Then the controls are finished out with a set of Pro Taper midrise bars, Domino throttle, PBM push button switches and some aftermarket levers.
Over the hand laid fibreglass seat, the foam is shaped to tie the rear fender and tank line all perfectly together and it’s then stitched up by Timeless Autotrim with the black gripper seat featuring a few trick red details. A bike like this needs the paint design and finish to be perfect, not over the top, but still capturing that classic DT livery as inspiration, and as always Justin at Popbang Paint knocked it out of the park.
Improved performance in every single way, flawless finish and craftsmanship, and an engine that sings that sweet two-stroke song. She’s not to be babied, this bike was built for a purpose, “I’m sure our rider will treat it right and have it dirty most of the time,” Tom smiles!
[ Purpose Built Moto | Instagram | YouTube | Photography by Nine Fivers ]