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I was looking for a cheap 250 when I heard about a Yamaha DT175MX with only 4000 miles on the clock going for £250. The DT175MX was the first Japanese road bike to have monoshock suspension and sold very well, mainly because of this. The early version had a five speed box, CDI ignition and a high level crossover exhaust, making a very attractive package for its day. The gearbox was replaced by a six speed item shortly after its launch. Final models also having a box section swinging arm.
This bike was 1980 V reg model with a six speed gearbox and tubular swinging arm. The tank was a little chipped and the right-hand footrest was missing, but overall it looked okay. A test ride revealed it was either running a bit rich or needed a decoke and a few bulbs had blown, but I was happy enough so I bought it.
When I got home I set about giving the bike a decoke. The six nuts which held the cylinder head on could only be removed after removing the exhaust, which in turn needed the petrol tank and also the seat removed. All except the exhaust were easy to remove, the exhaust requiring a little wriggling and twisting to avoid the upper frame tubes. The barrel is held in place by four threaded rods with very soft alloy nuts. Two of the rods were stripped of thread, the only way to remove them was by locking one nut against the other on what was left of the thread and gently applying pressure.
When I polished the piston crown, I found that the bike was already on its second rebore at 4000 miles! Probably a credit to the previous owner, I thought. Carbon only seemed to accumulate around the exhaust port, the piston and head only having a thin coating. On reassembly I bunged in a new foam air filter as the old one had disappeared. Foam filters can be washed out in petrol and oiled, it beats paying out £5 a time for a paper element.
When I ran the bike it would not rev above 5000rpm, with thick blue smoke trailing behind. Back in the garage, I checked the oil pump setting which had been set with washers rather than shims - the air filter had been removed to help it burn this oily brew and it also explained the two rebores. After fixing that, the bike would hit 5500rpm and take off like it should.
The DT does take a few days to get used to as pulling away below 4000rpm would bog down the motor unless the clutch was carefully fed in. Pulling away above 5000rpm, however, produced some spectacular wheelies. Once, pulling away quickly into a space between two moving cars with the aid of my friend on pillion, the front wheel became airborne by about a yard, but the bike was perfectly balanced so I just carried on, reaching third gear before the front wheel kissed the road. In fact, a good DT engine would lift the front wheel slightly when changing into second from third under hard acceleration.
In town and on A roads the DT does make a good commuter. It accelerates faster than many cars and can be nimbly manoeuvred between queues of traffic. On my daily ride through Nottingham, a Honda CB250RS would be left behind at each traffic light GP. Once on the dual carriageway, however, the DT would lose its initial acceleration advantage and the RS would quietly run past.
Dual carriageways are not what the DT was built for. At the redline it would pull 65mph dead, any head wind could take this down to 50-55mph with the engine screaming in fifth gear. Of course, chinning the tank cuts down wind resistance but at over 6 feet tall, I would look like a real prat, especially remembering one occasion when a CD125 Benly quietly sailed past with its rider bolt upright. This was my most humiliating moment.
In the subsequent hunt for more power I read that if I added Boysen reeds to the engine, then combined with the Stinger exhaust already fitted, power would increase by 25%. I bought the reeds, cut the reed block back as instructed and bent the reed petal stop back. When everything was together I only noticed one difference, it became less of an on/off motor at 5500rpm, sort of taming the power band. Top end, economy and acceleration all remained the same.
Economy was poor, but I did seem to be riding around at maximum revs everywhere, so maybe 52mpg wasn't all that bad. At 7000 miles the exhaust pipe cracked clean in two, just where it exits the barrel. This also happened to a mate's bike, so it may be the weakest point on the system. A new one cost £65, but luckily Mutsui were offering pre 1980 parts at half price, so £32.50 wasn't too bad.
When I bought the bike the chain was brand new, so I looked after it with aerosol lubricant every few days and boiled it in Linklyfe every few months. With this tender care it lasted 7000 miles. Without it, I would imagine 4000 miles to be more likely.
The front forks are very strong, as I found out when I ran into our house! An out of control wheelie being the cause. They are easy to drain of oil and refill via screw-on caps, unlike some Yamaha forks with awkward circlips to remove. I used to fine tune the forks, finding SAE15 oil gave the best ride, whilst not producing too much dive under braking. A word of warning, though, make sure the forks are fully extended before removing the caps, as the springs are very long and powerful, launching the cap and spanner suddenly around the garage.
The monoshock, on the other hand, is quite a crude device by today's standards but it does work after a fashion. The upper pivot catches all the crud thrown up by the back wheel and needs regular greasing, otherwise it becomes stiff and affects the monoshock's operation. Another reason to keep it well lubricated is so the swinging arm can easily be removed every 12000 miles to replace the plastic roller, which protects the swinging arm from being massacred by the chain.
With winter fast approaching and the Pirelli tyres looking shoddy (7500 miles rear, 8500 front), I decided to buy a very trick pair of Michelin T61s - they look like motocross tyres and suited the bike really well. I once (and only once) grazed the footrest down on a sharp left-hander with absolute confidence, looking more like an ice racer. However, 4500 miles rear tyre life was a steep price to pay.
One dark cold morning, Derbyshire awoke in the grip of a snow blizzard and most people stayed in bed. I was overjoyed and couldn't wait to take the DT out. My ego was a little deflated, however, when to get up our drive I had to run alongside the bike. I carefully rode along the country lanes in second gear, with the just adequate 6V headlamp picking out a lonely trail. When I reached the main road, conditions were a little better so I went a bit faster, my confidence growing as I reached third and fourth gears.
I arrived at the bottom of a steep hill with cars abandoned all over the road. As I rode up the hill my back end would step out occasionally, so I stopped to lower the tyre pressures to 10psi. A chap rode slowly past on a Honda stepthru and shouted, 'Ha, get one of these, boy, a lot better than that fancy tackle.' I looked up to give a smart reply, when his front end slid away and he landed in a heap next to me. He got up unhurt but with severely dented pride as I burst into fits of laughter.
I rode on through Langley Mill and on to the dual carriageway, following cars at 30mph, single file on the inside lane. The DT felt very stable and eventually the outside lane tempted me - 35, 40, 45, 50mph on the virgin snow, rock steady until I hit a ridge of snow. The dance that followed must have entertained the car drivers no end, but somehow we stayed upright.
Winter had just ended when the DT developed an electrical problem, any light turned on would shine extremely bright and then blow. I bought a black box which does away with the battery and replaces the voltage regulator.....out on the road everything was okay until I stopped and noticed that white smoke was pouring from the box as it melted.
Eventually, I started to follow the vital wires until I came across a small piece of plastic between two spade connectors, located on the frame under the petrol tank. One of the connectors was corroded so it was cleaned and greased - everything worked okay after that. This insignificant piece of plastic was the rectifier, a vital component which had caused all the trouble.
After ten months the bike started to rumble from the bottom of the engine, the main bearings were shot at 10500rpm. When I split the cases, all the selector forks fell out. Five evenings work and I was back on the road, running the engine in for 500 miles, revving between 4-5000rpm. During that time it returned 77mpg but soon returned to the usual 52mpg when ridden normally.
I soon sold mine, out of town it was not much more use than a RXS100. On buying a DT the points to check are monoshock linkage, the exhaust where it exits the barrel and the wheels for dents. The oil pump is also known to fail through corrosion as rain water trickles in through the cable entry point and can't get out. And, of course, check the electrics. It is a fun bike but needs an hour's maintenance every week to keep it reliable, and a decoke every 2000 miles even if you use low smoke oil such as Belray S17. As a weekend toy, though, it's a lot cheaper than a TDR250.
Steve D.
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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
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In its day, ten years ago, the Yamaha DT175 was one of the most successful trail bikes on the market. Its single cylinder stroker motor put out enough power to keep the 240lbs in adequate motion, but it was never so vicious or unwieldy as to throw off novices at the first taste of the dirt. The DT125 was a bit too peaky and gutless at the same time, whilst the 250 was a bit too heavy and powerful for those without yonks of experience.
Buying a ten year old mono-shocker was quite an interesting experience. The bike'd been resprayed black, had polished cases and wasn't so dented that I could dismiss the owner's claim to have never ridden off-road. He admitted that the front end was off an earlier model after he'd had a mild prang with a bus. Running a magnet over the petrol tank revealed lots of filler! £250 changed hands, not bad as the engine didn't rattle and there was a new MOT.
The ride home was in the dark. The lights were paltry, just about adequate for warning car drivers they were about to run over me. After ten miles of wrecking my eyesight I was able to test the trail abilities when we ran off the road. On Metz enduro tyres the DT was impressively stable. The only problem was that I hadn't spied the log laying across our path. When the front wheel whacked into the wood we came to a sudden halt. I was sent flying over the bars, which smacked my thighs. After a ten minute cursing fit I was able to walk again. The front wheel was still straight despite the force of the impact.
The engine was a relatively sane unit, able to run between 1000 and 10,000rpm without any glitches, although it'd become more interesting from 6000 revs onwards. The exhaust was patched, rusty but intact, an essential ingredient for long engine life and good carburation. Expansion chambers, and the like, turn the bike's moderate taste for fuel and oil into an addict's desperate need for crack.
After the crash I sped home at all of 10 to 15mph, peering disconsolately over the bars to see where I was going for the next thirty miles. At home I had trouble adapting to the bright lights of the living room, searing brain pains and strange visions for half an hour. There doesn't seem any easy way of upgrading the pathetic electrics (the horn was useless and there weren't any indicators).
The other immediate downer was the front drum brake, which had so little power that I was sure it'd come off a 125 or maybe even a nasty fifty. Every time I tried to use it hard the lever came back to the bars and the retardation faded away to nothing. Coming home in the dark, speeds were so low that the lack of braking wasn't a worry, but rushing the bike through heavy traffic, where it was in its natural habitat, proved as frightening as putting a hand into a crocodile's mouth.
The shoes were down to the rivets. As I didn't know from which bike the wheel came, it was a matter of running around breakers until a used pair were found (for three quid). That made braking tolerable up to 50mph, but it'd still do a disappearing act if used in anger from greater speeds. The rear drum was one of those on-off devices, which helped in the dry but sent the DT into wild slides if touched in the wet.
Engine braking was minimal, but the motor made a nice burble on the overrun with amusing back-fires thrown in to keep the general populace awake. They were less elated by the smokescreen, with oil going through the engine at more than a pint every 100 miles. The tank didn't hold very much, so I had to check it every day. Despite its consumption of oil, the reed valve motor would run along at minimal revs without clogging up the spark plug and starting was a first or second kick affair. Impressive on a motor that had done over 35000 miles even if it had been comprehensively rebuilt 5500 miles before (the bike came with a wedge of supporting bills).
After becoming used to the brakes, I found it a more than adequate town hack. Plenty of speed and enough suspension travel to soak up the bumps. It was also quick turning, just breathing heavily was enough to have it doing a 90 degree turn. Two strokes of this kind of capacity are ideal for town work but come close to being dead meat out of town, where lack of go above 75mph makes them sitting ducks for caged maniacs.
Within about 600 miles, the crankshaft's oil seals were blown, vast amounts of oil being burnt off. As it's only a two-stroke single it wasn't that big a job to do, except that all the engine screws had corroded in solidly, needing the hammer and chisel routine. Some screws snapped off and had to be drilled out, others took out most of their threads on the way out. The steel and alloy had interacted to form an almost solid substance. I only whacked my thumb once!
Once I'd fixed the seals the motor was clean running and quite adequate for pulling wheelies, which got me pulled over. I told the cop I was practising for off-road work and he let me off with a warning. I felt duty bound to head for the nearest council tip, which was surrounded by barbed wire and patrolled by security guards. I found a hole in the wire and amused them no end by avoiding capture for half an hour.
The DT ran over the rough ground in a generally splendid manner. Back wheel slides were fantastic fun and it'd wheelie at just the pull of the bars. The tip was full of tramps, or at least they looked like tramps, who were picking through the mountains of waste. I'd charge at one of these dubious characters, sending him flying, head first into a pile of muck. Hilarious.
A group of weight lifter types with big sticks had congregated around the hole in the wire. I charged them, too, screaming a lungful of abuse. They moved aside, but I hit the wire slightly out of kilter, metal tearing into my jeans, jacket and lid. I got away with some large lacerations in my thighs which needed some stitches. I was impressed by the way the Yam had refused to chuck me off.
Proper off-road work was more difficult, especially if it was wet. My techniques were fairly rudimentary, more experienced trail riders might find the going easier. The back wheel liked to bog down in mud, a vast amount of revving and clutch slip needed until it would free up. I was soon covered in a layer of mud, as was anyone else within a 100 yards. Whilst I could get the front wheel way up in the air, the back wheel would often snag on the obstacle, causing the whole bike to fly backwards and land atop my startled, flattened, screaming form. The easy solution was to ride at 10 rather than 50mph.
Then there was the question of the good old water. Riding across a foot deep stream the motor cut out. I put my foot on what I thought was the stream's bed but turned out to be a deep hole. The bike and I fell into the raging torrent. By the time I'd dragged myself out both DT and I were soaked through. The bike took even longer than myself to dry out!
The same thing happened on really wet days. On damp surfaces the tyres always felt a little unsafe, as if there was insufficient mass to keep the DT on the road, letting it float like a duck instead. But that was the least of my worries. I was more concerned with the way that the vast amount of spray let past by the highly mounted front guard was soaking the engine. By the way, five minutes in the wet or off-road would quickly ruin the appearance of the DT. Replacing the HT lead, coil, cap and spark plug reduced the cutting out to a stutter. After I decided to give up trail riding I fitted a proper mudguard on the lower part of the forks which stopped most of the spray from hitting the motor; end of problem.
The gearchange action was clean, but the clutch, perhaps because of all the abuse it'd taken, started to slip 7500 miles into my ownership. It was another battle with the engine screws to fit some pattern plates. That was 3000 miles ago and now there are some nasty rattles from the barrel, which indicates it's about due for a rebore. Top speed is not much more than 60mph and the smokescreen is back in force.
As for consumables, the tyres lasted 10,000 and 8000 miles, front and back respectively. The chain only did 6000 miles, needing constant care and attention. The sprockets were just as far gone. The brake shoes haven't worn out yet and the brakes need hardly any attention, though they are not much cop. Fuel's around the 60mpg mark when the engine's in good condition and about 45mpg at the moment. All the chassis bearings were replaced just before I bought the bike and an excess of grease is still in evidence (the back end's bearings wear quickly if neglected).
All in all, it's a robust little machine that's ideal for snapping around town. The engine hassles are easy to fix and, well, pretty typical of a stroker of this era. I wouldn't pay silly money for one, but as a bargain basement hack they make the grade.
Tony Klein