Bringing you the world's best cafe racers, trackers, scramblers, bobbers & custom motorcycles.

1976 Yamaha DT400

Posted on December 11, 2013 by Andrew in Bobber. 22 comments

By guest writer Ian Lee.

“I have an idea, let’s make it a two stroke bobber’. And that’s how the build started. From a rusted lawn ornament, the 1976 Yamaha DT400 was changed into the impressive piece of machinery you see before you today. Built over the course of three months, using original parts from the bike and anything else that fell to hand in the workshop, it was a failed attempt to enter the Rusty Kustoms Biker Build Off. Mind you, we use the term ‘failure’ in the loosest sense of the word. Built by Tom Armstrong, Matthew Blythman and Steven Blythman; a spray painter, industrial designer and civil engineer respectively. This bike is proof that you don’t need alot of money or time to build a unique custom motorcycle – a six pack of beer helps though.

After seeing the MX bike languishing in a friend’s front yard, the trio decided it would make a good base for a project bike. With a leg sticking out of bed, covered in years of rust and bird droppings, the DT was a poor sight. Purchased for a six pack, dumped unceremoniously at the back of the shed, it took a quiet night and some amber inspiration to get the project underway, but once it did, magic happened. It was at this point that the two stroke bobber concept was born, an angle grinder used as a means to this end. First things to be surgically removed were the seat and swingarm. A couple of design ideas were decided to be adhered to, like wide grip handle bars, retaining the knobby tires and giving the tank artwork a ‘DT’ feel’.

Stripping the bike back to bare bones, the frame was mounted on a homemade jig to keep everything inline, and the fabrication of the hardtail begun. Much thought was put into the stance of the bike, with a real dirt tracker style aimed for. The final result was an overall length increase of four inches, and the front end dropped by three inches. A new seat was handrolled from aluminium sheet, with Steve producing the cushion on his mum’s sewing machine, having no prior experience in sewing. The headlight is half of a set Tom bought for his Ford Falcon in Vietnam, but after smashing one decided to put it away for later use. Lighting at the ass end is thanks to a 60’s dragster, and mounted on the TZ rear guard is the Ebay copy of an old Japanese racing plate.

The shining light of this build has got to be the fuel tank. Utilising the average looking factory tank, the sides were scalloped out, and the section around the filler dished. Once this was done, Tom ‘flexed his bog skills and then applied the paint with some heavy flaked graphics to resemble the bike’s original tank design’. To round it out nicely the trio used close mate Matt Bailey to apply some appropriate text around the filler. Poking out behind the tank is the exhaust system, the original header matched to some offcut mandrel pipe. Mounted in the frame is the oil tank, donated by an old Victa lawnmower.

Once the frame was completed, the hunt for an engine was on. Sourcing a powerplant from a ’75 DT400, it was mounted in the freshly modified frame. All was for nothing though, as the engine just wouldn’t run. With fuel, spark and air getting to the engine, the boys were stumped. However, a prior thought that such an event might occur prompted the purchase of a backup bike. The replacement Suzuki TF125 was built in the wee hours of the final night before the comp, took first first place in the motocross comp, and almost succeeded in taking the rider’s foot off halfway through the victory lap.

Once the dust had cleared from the Rusty Kustoms Biker Build Off, the new target was decided to attend the Chopped Rod and Custom with a running machine. The starting issue was traced to a faulty CDI unit, so the bike was fitted with a points ignition system. After being wired up and the points set, the bike started first kick.

From a non runner bought for a 6 pack of beer, the trio have rebirthed this 70s Japanese enduro bike and turned it into one of the most original two-stroke bobber dirt trackers we’ve seen.

Photography by Jason Lau 

  • tomo8r


  • Probably the most unique exhaust routing I’ve seen all year. Love it.

    • Scott T.

      I’d be curious to see a pic with a rider.

      • Ichiban Moto

        yes, please

    • tincantroubadour

      I don’t think it’s a ’76. I think it’s a 77 or so; it’s the stock pipe, just cut off and turned out

      • Tom

        well it is a 76 and it isnt the stock pipe cut, its a bent piece of stainless.

  • theothermanxman

    Yes, yes and yes.
    How do you do that to a tank? Is it just cutting and welding?
    God knows what its like off tarmac. You would stop looking cool
    and start looking terrified pretty quick.
    Love it though.

    • ccc40821

      Carefully beating the sides of the tank into this shape is possible, if time consuming. Dunno what the builders did here. though.

      • Robert F. Russo

        Don’t think you could hammer it into that shape. There’s no way to get it on a wheel or hammer to smooth it out. Usually, the sides of the tank are cut out and replaced with new or, if you can get a thin enough cut, the pieces are flipped so the curve is inward and then rewelded back onto the tank.

        • Alex Bredkjær

          At 16.24 starts a scene that might give you an idea how it can be done – I’m not sayning it is the ONLY way to do it, but it is A way.

        • davmo

          +1 on cutting and flipping sides.

  • Tony

    I have been throwing the idea of a mid seventies big cc dirtbike build around in my head for a while now and this is a lot like what my design was shaping out to be. My only question is: I wonder how the two stroke power is since the exhaust is so much shorter now and the expansion on the end is not as tight anymore. Either way sweet looking build

    • Tom Armstrong

      it goes great, we left the smaller stinger pipe underneath the larger, it actually surprised us how much band it sill has

      • tincantroubadour

        Considering the smaller stinger is hiding in there, now with no muffler, it may go alot better than stock – these were really corked up with the crack-down on 2T in the later 70’s

  • John in Pollock

    Best bike in ’13 IMO. Love it.

  • Jonas Vandersmissen

    rear brakes?

  • revdub

    Looks like a lot of fun to me. Love that tank.

  • Matt

    Hey guys. Thanks for all the response! To get the tank like it is, Tom carefully beat in the sides with the side of a rubber mallet. Sitting and riding on the bike is very comfortable, however you need to keep an eye on the exhaust burning underneath your thigh. As for power, without ever riding a standard DT400 with the full exhaust it is hard to tell, but all we know is it is damn fast- the small exhaust outlet is still under the mandrel bent exhaust tip to retain the back pressure. Thanks for the comments, and thanks for the feature Pipeburn!

  • Septic the Sceptic

    I have an idea, let’s ruin a perfectly good bike with a bunch of hipster bulldust.

  • For some primal reason I want to ride this bike very, very much. Best 2-stroke chopper in a long time.

  • Bob Ratcaf

    Had one of these for a while… in a less ‘bobberised’ trim. Used to love killing cruiser bikes off the line from the lights with wannabe dragsters. It seems so unassuming but man it hauls. This version is much prettier though, well done.