The test ride was impressive. Every time I hit the throttle the front wheel reared up in the air. I soon convinced myself that there could be little wrong with the two stroke single cylinder engine. The rest of bike had a stripped down look, anything, like mirrors, indicators or stands, not absolutely necessary for forward motion thrown away.
Ten years old, it had received enough cosmetic attention to pass as a two or three year old machine. Even the wheels still shone brightly. The owner muttered something about having opened out the ports and put in a racing piston. The far from standard high-rise expansion chamber emphasized its nasty nature. Mine for £375. How could I resist?
Buying a ten year old stroker is not the wisest of moves but I'd had a lot of experience with smaller Yamaha strokers so felt equal to the task. What I had not realised with the tuned DT250 was that it only worked under acceleration. Trying to roll along at a constant speed caused the motor to hunt, stutter and backfire. Whacking open the throttle, on the other hand, produced a vivid, startling burst of acceleration that eventually had the speedo needle quivering around 95mph.
The other thing that I had not noticed on the test ride was the vibration. This was a relatively low tech single cylinder motor without any balancers that had probably done something like 50,000 miles and had God knows how many rebuilds. And, it wasn't the kind of mild vibration that faded into the background after a little while.
The first fifty mile trip was enough to leave my fingers tingling, wreck the innards of my ancient Timex watch and lose the numberplate. Okay, I had been riding like a juvenile delinquent with the throttle on the stop, the engine emitting the kind of banshee wail that even with a full face lid and pair of ear-plugs left my head ringing for the rest of the day. Hmmmm. I was obviously getting a bit too old for this kind of total self-indulgence.
As I suspected, the exhaust was of the straight through variety. I just knew if I tried to modify it the carburation would become even worse, so I left it alone. Some thick handlebar grips were added and a new numberplate made up (attached with Loctite and spring washers).
The next ride revealed a secondary problem from the vibes - the lights kept blowing. Not that the front lamp did much to illuminate forward progress even when working properly. Every half mile or so I had to glance backwards to check if the rear light had blown. A lot of this nastiness was down to the battery being chucked and a large capacitor put in its place. Had a working horn been fitted it would doubtless have overloaded the minimal electrical system.
There wasn't an ignition switch as such, the motor had to be stalled in first gear to stop it. Starting from cold was a dangerous bump start affair that more often than not ended with me rolling around on the ground in a wrestling match with the DT - just as well it could not have weighed more than 250lbs. Three or four kicks were sufficient if the engine was hot, but with a tendency to stall at low revs that was rather excessive for my taste and leg muscles.
If this all makes the Yamaha sound entirely impractical, you'd probably be right but it was a hell of a lot of fun to ride hard and fast. A lot of this joy came from its lack of mass, taut mono-track rear suspension and a hefty pair of forks (not stock) which made the terrible stroker a pleasure to throw through any kind of swervery.
My mate has a GPz550, no mean handler itself and with about twice the power. I enjoyed myself immensely racing with him down tight back roads where if either of us hit 70mph we were liable to ride off the road. As long as I kept the power on by flicking up and down the surprisingly excellent gearbox, the GPz could be kept at bay. But, if I selected the wrong gear ratio the engine would sulk until hurriedly knocked down a couple of cogs. The DT was an exhilarating bike to ride short distances but a very tiring one for more than 50 miles.
The easy way the bike would wheelie meant that for hard cornering I had to crouch over the bars in a most ungainly, not to mention painful, posture. Letting the bike wheelie when accelerating out of corners was not recommended as the bars shook like the front wheel was about to fall out.
The disinclination to do long distances was just as well, really, as it would burn a pint of oil in a 100 miles and a gallon of fuel in 35 miles. The chain was reduced to a string like mess in about a 1000 miles and the back tyre shredded in about twice that distance. All down to the compulsory full throttle abuse.
Town riding could be a breeze or horror time. As long as the engine was being revved there were no problems. However, streets full of cagers meant that it was impossible to keep that up for any length of time. Trying to ride at a constant pace or, worse still, backing off the throttle, turned the bike into a snarling brute that threatened to stall dead or misfire loudly. Occasional huge detonations caused jittery shoppers to run for their lives.
As might be guessed, the DT was not my only bolide. I had a CBR600 for the serious stuff and an ageing GPz305 for the commuter chores. The DT was more a throwback to my lost youth than anything else, so therefore a more than viable means of amusement. I did about 4000 miles of trouble free hustling before any serious faults turned up.
The first was the expansion chamber cracking up. This could not be ignored, as well as making even more noise it put a 5000rpm flat spot in the already demented power characteristics. I got a mate in the car trade to wave his welding torch in its direction. Rather than fixing the problem it left a bloody big hole in the exhaust. Took him about an hour to weld a bit of plate over the gaping abyss.
Then the swinging arm bearings went. Before their demise became evident the DT showed its mettle with some vicious speed wobbles. On one occasion my mate on the GPz was behind me and reckoned that I was lucky to be alive - the frame looked like it had turned into a big bit of wobbling jelly. I did the bearings in the mono-shock linkage at the same time as they were also a little slack.
The front end wasn't stock, looked like it came off an XT600, had stunning braking and was rigid enough to take even the most inept wheelie madness in its stride. Grabbing a fistful of brake was often the only way to save the bike from the mad manoeuvres of cagers in town when the engine sulked and all forward motion threatened to do a runner.
In that vein, riding in the wet was not something that I would recommend. Everything was just too vicious to risk the depredations of wet, greasy roads. Water would also attack the electrics, and with only a single cylinder just the slightest degradation of the ignition circuit was dangerous. Water ingress would also blow the single fuse until I put a nail in......A week later the generator burnt out, a used replacement cost all of five notes.
The engine had always pinged, rattled and clattered with no apparent ill-effects. Such was the exhaust racket that I had to get down close to the engine just to hear those noises. One morning, though, a distinct knocking noise was added to the cacophony. I ignored it for a while but rode with my left hand on the clutch just in case. A week later the motor seized then freed up again.
I motored home gently, pulled the motor out (15 minutes) and tore the top-end off (10 minutes). The crankshaft bearings were shot, as was the small end. Rebuilt crankshaft time. That was all a week ago, so the motor is in bits at the moment. I intend to rebuild it in slightly milder form with proper silencing.
Mark Hamilton