YAMAHA YZ490 Production history, specs & general overview….. I have always had a bit of a soft spot for the Yamaha YZ490, a purposeful & uncluttered machine, it looks like it can get the job done, a bit like a sledge hammer & once the big YZ has been knocked into shape it takes about as much looking after as a big lump of metal wedged on the end of a big stick. As the years have rolled by I have grown even fonder of the big air hammer, to me it seems to have a foot in both camps, the simple air cooled engine harks back to the good old 1970s while the later version mono shock rear end puts it firmly into the Evo 80s. When you see one today its almost impossible not to think about great 500GP riders such as Hakan Carlqvist & their famous blue & white Yamaha race shirts.

Now I know what you are probably thinking, you remember all the problems the bikes had when they first appeared & how the motocross magazines & testers at the time basically wrote the bike off, especially as the YZ465 it replaced had been regarded as a pretty good machine. The press seemed to get even more critical & then totally disinterested as by the mid 1980s other manufactures had started to produce all new & exciting water cooled 500cc machines. I like you have heard all the stories about riders who jumped off a 250 & expected the extra horse power of the big YZ to shave a few seconds off their lap times, only to find that the bike felt heavy & was reluctant to turn. In the end a rider would find his lap times had got slower & the big bike took a lot of energy to muscle around. The love affair was soon over, the bike was sold on & the rider returned to a much easier & fun to ride 250. In fact this scenario goes for pretty much all big bore motocross machines from the period, once people figured out that the new Evo 500 machines had more power than the average rider could handle the second hand value of even fairly new big bore machines took a hit.

The passing of 30 years has made a big difference to how the vintage motocross racer views the Yamaha YZ490 & all the other 500cc two stroke machines, more often than not it`s now the big capacity machines that attract the most interest & carry the biggest price tags. Oddly, the fact that most of us could not handle the machines when they were new & we were younger / fitter, does not seem to matter at all. Can the vintage racer of today iron out all the problems & make the big YZ an easier bike to own & ride ?  Judging by all the machines I saw & photographed at various major race meetings in 2015 I think the answer is yes, many riders are now spending time & money on these bikes & getting good results. The passing of 30 years has given us two great things, firstly the accumulation of a lot of knowledge & experience regarding these machines & secondly the fact that some kind soul invented the internet so all that knowledge & experience can now be easily found & shared.

1982 YAMAHA YZ490J

1982 The New Yamaha YZ490 J Hits Town……Obviously when any new motocross machine is released it is immediately compared to it`s predecessor so the increase of about 3KG in weight compared to the old YZ465 was immediately noted & not liked, the reluctance to run a tight line through corners did not impress also, a bulky fuel tank restricted riders from getting forward & weighting the front end, which seemed to be the only way to make the bike turn. Over the years people have remarked that the “J” series 4 speed transmission, with its new, physically wider & stronger cogs, felt “gappy” compared to the old 5 speed found on the YZ465, looking back this all seems very odd because Yamaha kept the same gear ratios as before, all they did was to just leave out the old 1st gear cog from the previous machines transmission, the mystery deepens when you read the original YZ465 magazine reports from back in the day, as far as I can see nobody complained that the YZ465 suffered from “gappy” transmission ratios. Was it just a case of miss matched front & rear sprockets on the 490 when new ?  Vibration was another gripe with the original YZ490 & the problem pretty much remained through all the years the bike was in production, on the subject of vibration, owners should keep a watchful eye on all fastenings especially the motor mounts on the early “J” series, these were considered to be manufactured a bit on the wimpy side & can get seriously damaged if the bolts become loose, so be warned. Air leaks were reported, not good for a brand new machine but a relatively simple thing to fix for todays restorers / owners, not having a water cooled head & barrel makes the job easier. Unfortunately there is no getting away from the fact that when Yamaha released the new “J” machine it was equipped with suspension that was far to softly sprung both at the front & rear, again this lead to a lot of criticism. Poor quality control at the factory gave owners even more headaches, things like chain guides that were mounted off centre & chain adjustment marks that did not line up lead to constant drive chain problems, plus a rubber air hose that was too long & kinked which then upset Yamaha`s “YEIS” or empty can “Boost Bottle” induction system & caused the bike to bang & pop. The problems that the YZ490J will most be remembered for among the vintage motocross community is the dreaded “PING” or pre ignition & a 38mm carburettor that you could not jet correctly, blubbering & a general lack of crispness when accelerating out of corners was the issue. Owners would jet the carb lean & reduce the blubber & ping but then ran the serious risk of a seizure & if they jetted things on the richer side they were rewarded with fouled plugs & even worse performance. The bottom line was Yamaha had produced a motorcycle that even when brand new needed quite a bit of TLC & more money spending to get it sorted out, it did have a great engine with monster power but only if a rider could find a track that had straights long enough to get the thing wound up, cleared out & into the meat of the power band.

1983 YAMAHA YZ490

1983 saw Yamaha introduce it`s revised Mono-x rear suspension system, very similar in operation to the Honda Pro-Link set up. The upright connecting rods were done away with & now all the forces generated by the upward movement of the rear wheel were delivered to the spring / damper unit at the bottom rather that at the top, the new rear suspension system also saw the shock unit mounted in a more upright position. After reports of clutch problems on the “J” series it was decided to revert back to a steel clutch pressure plate & in a bid to tackle the machines weight problems changes to the frame, wheels & various suspension components saw a reduction of around 8KG. Efforts were made to sort out the motor, Yamaha did managed to move a little bit of the power down to the bottom & mid range, though the majority still stayed way up high, it was defiantly a real start straight weapon, if a rider had the talent the bike could get them to the first corner ahead of every body else. The motor would still ring, ding & ping but buyers & the motorcycle press gave the revised machine a slightly easier time.

YAMAHA YZ490 1984

1984 If you think that all YZ490 motors were pretty much identical then think again & check parts compatibility especially if you are ordering in new or second hand stuff from the other side of the world, 1984 saw the motor change to a new exhaust centre port design. In a bid to get the power exactly where riders wanted it the exhaust & intake ports were made narrower, the exhaust by 2mm & the intake by10mm but the internal cylinder transfer ports were made 4mm wider, added to this was a new read valve design that now sported eight petals instead of six & a new 40mm carburettor to replace the old 38mm one. Unfortunately the new carb was set up completely wrong at the factory, so owners had to swap the slide, needle & pilot jets before they could start to enjoy their new toy, this year also saw Yamaha beef up those fragile motor mounts. As far as the chassis was concerned, the front down tube on the frame was redesigned to accommodate the new centre exhaust port & the steering head angle altered. Other changes included shorter fork stanchions, less offset on the new triple clamps & a new, lower mounted & narrower fuel tank, this was to help the rider slide forward easier & weight the front end when cornering. So far all these updates seem pretty good & indeed once the carb problems had been sorted out the latest offering had a better spread of power, if you were feeling lazy you could circulate most tracks by using only two gears or if you had the skill, strength & were brave enough you could twist the throttle & pretty much blow away anything else other manufactures had to offer. Two things that did spoil the plot were yet again the suspension was criticized for being too soft & the other potential problem that buyers & restorers today should be aware of is some bright spark came up with the idea of what Yamaha christened “Z Spokes”, basically two spokes that when joined together formed one long spoke that stretched from one side of the rim to the other, the central connectors zigzagged through holes in raised lugs cast around the edge of the hub, this new system had the effect of reducing the number of spokes used in the wheel but for the poor old buyer / restorer 30 years later down the line this set up is a potential problem because for one reason or another the cast lugs can break off the hub. I have talked to several wheel builders over the years & all of them thought the idea was a bad one & more trouble that it was worth, even when new.  I don`t know if a damaged  hub can be repaired but it`s defiantly something to check if you are thinking about buying one of the YZ models from the 1984 – 85 period.

1985 YAMAHA YZ490

1985 This is the year that machines for the American market changed from being yellow to white & looked the same as European models, another easily spotted change was the front wheel now sported a disc brake. A less obvious Yamaha innovation was the new, Brake Activated Suspension System or “BASS” for short. The idea was simple enough, when a rider pressed on the rear brake pedal, it pulled on a cable that was attached to both the pedal & a valve on the rear shock, when activated this valve mechanism altered the compression dampening effect on the rear suspension unit. It was designed to reduce the old “YAMAHOP” problem by helping to keep the rear wheel in contact with bumpy sections of ground, it never really worked & could cause all sorts of problems especially if a rider dabbed the rear brake while travelling fast up the face of a jump, a lot of owners just disconnected the cable from the pedal & quietly forgot about it. On the plus side, the frame got a bit lighter, the bike got stronger wheels, clutch modifications made it easier to operate & at long last the factory managed to supply the customer with a bike that had a carburettor that was jetted somewhere near right, in fact rumour has it that this, along with the redesigned kick start made the bike an absolute breeze to start. It would still ring, ding, ping & vibrate but you can`t have everything !

Development slows down.. At this point the factory decided to stick to the same basic layout & motor until the model was retired at the end of the 80s, the main reason for this was Yamaha, as well as all the other manufactures that produced machines for the motocross market, could see that sales globally were going down, especially for the big capacity models. As much as the fans loved to see their 500cc heroes thundering around the GP circuits of the world, when it came to buying a machine for themselves the majority purchased 250cc or smaller capacity bikes. By the middle of the decade Suzuki had packed up all together & no longer produced a big bore 2-stroke & it may have taken a few years more but eventually even the mighty Honda CR500 & Kawasaki KX500 fell pray to the same sort of treatment as the big air hammer, receiving just a new set of graphics & a few very minor updates each year. By the time the 490 rolled into it`s final year or so of production various changes had been made along the way, the “BASS” suspension had been discarded & replaced with a better unit, the springs were still a little on the soft side but overall the front & rear suspension now handled whoops, hard landings & rough tracks much better. Those troublesome “Z” spokes had been chucked in the bin a while back, the front brake disc had increased in size to 230mm & the wheel rims were now silver & not gold in colour. The motor still pinged & vibrated but in 1986 that elusive 5th gear had reappeared in the transmission, the technicians back at Yamaha had also managed to give the easy starting motor a better spread of power from the bottom right through to the still very powerful top end but one things for sure, what ever they did to achieve this, it probably did not cost a lot to do !  Its sad to say but for the last few years of it`s production the motorcycle press, particularly in America, had the YZ490 marked down as a bit of a “Play Bike” & not a serious motocross weapon for an expert or pro class rider. This was not such a bad thing for riders in the states as they had a lot of space to play in, desert & forestry trails etc, the big Yam could happily turn it`s hand to all sorts of riding. The bike had & still has many fans all over the world & luckily many of them took no notice at all of what the magazine test reports said & carried on racing the big Yam in motocross events.

I thought you were dead !!….. Like so many other dirt bike fans around the world I could not believe my eyes when in the spring of 1991, a year or so after we all thought the 490 motor had gone for good, pictures emerged of the new Yamaha WR500. Like a zombie that had crawled out of a grave, that big 2-stroke air cooled YZ490 engine was back again ! Although their was still a hint of ping, ring & ding, Yamaha engineers had been busy making modifications to the cylinder head, exhaust & ignition to produced a motor that had extremely good power characteristics right through the range. This revitalised YZ490 motor, now painted silver, was slotted into a new frame that had been based on a YZ250 item. At the front was a set of Kayaba upside down forks & at the back we found the same suspension linkage as used on the YZ250 along with a shapely looking swing arm & rear disc brake. The white body work looked bang up to date with it`s razor edge rear fender etc, only the fins on the old air cooled engine gave the game away. Anybody who thought that “WR” stood for “Wide Ratio” transmission & the bike was aimed at serious Enduro work was wrong, the five speed gear box was the same as the one used in the old YZ490. Although the motorcycle press of the day again tagged it as a play bike it still looked the business & in the real world of clubman motocross racing it had what was needed to win races, apparently Yamaha did not manufacture very many of these wonderful machines, so today they are quite a rare beast. I will never forget a sunny Sunday morning in 1991 as I waited in one of the queues for scrutineering with my 87 CR250 ( which I thought at the time was an absolute fossil, due to it being an incredible 4 years out of date ! what an idiot I was ) when all of a sudden in the other queue a guy appears pushing a brand new WR500 Yam, it was still showroom clean, the sun glinted off the spokes, the young lad checking the bikes over said “it`s brand new, what should I check ?” another voice said “everything” so the lad gave it a half hearted once over & then stuck a pass sticker on it. I must say that if it was the first ride out on the bike for the lucky owner, the AMCA track he chose for the machines debut was an absolute bog hole, the narrow track occupied an incredibly small area of land on the sides of a steep valley, once you had bounced your way down one steep hill side you only had about 10 yards of flat, straight but very sandy track that also included a small stream running across it before you had to tackle an incredibly steep, slippery & long climb out. If the weather was bad a queue of stationary riders would quickly form as each rider waited for their go at the climb, I will never forget the deafening sound bouncing off the walls of that narrow valley as 125 & 250cc 2-strokes screamed up the hill, engines revving flat out in second gear, slowly creeping upwards, rear wheels spinning like mad looking for grip, a group of helpers would gather at the top, ready to grab the front wheel of any bike that came to a halt near the top. O happy days, not. Sorry for wandering off into tales of old but the story does demonstrate what local amateur motocross racing in the UK was like for your average clubman rider back in the 70s, 80s & 90s & what the big heavy, hard to turn YZ490 had to cope with. The tracks were quite often short, narrow & laid out on terrible bits of land, a far cry from what we get to ride on today, I well remember going to a circuit  that included a 200 yard section of 3 foot high bracken stretching the whole width of the track, the riders were expected to just charge through it at race speed, absolute madness ! it was the afternoon by the time all of it had been trampled flat & any hidden dangers revealed.


Conclusion…. Before condemning the Yamaha YZ490 as a failure & agreeing that it deserves it`s place on that list of “Top 10 Worst MX Bikes Ever Made”, I must admit that constantly seeing people refer to a list that was compiled by one or two American gentlemen many years ago is beginning to get a bit tiring. No, I think we should stop & take a look at the situation from the point of view of a rider based in the UK today & is someone who wants to race the Evo class. We must remember that a rider is restricted to using a bike manufactured between 1980-81 to 1989 & if like so many of us he wants to emulate his heroes that raced the 500 GPs on big bore 2-strokes, then a riders choice of machine is further restricted. If he, or she, takes a practical approach & thinks about purchasing a machine that is “A” easy to find & more importantly “B” easy to find spare parts for, then certain rare bikes that had a short production life will have to be crossed off the shopping list from the start. If they removed all machines from the list other than those that did not have faults from new & were perfect straight out of the box, then I think they would end up with an extremely short list of possibly none. Once you start to research bikes model by model it`s surprising how many, even from the likes of Honda, had the magazine testers of the day scribbling unflattering remarks such as “Terrible gear box” Honda CR45O, “The King Of Ping” slightly later big bore machine from Honda & “Too much power, it`s uncontrollable” one of the early water cooled CR500 models, again from Honda. Kawasaki`s early 80s big bikes faired little better, the KX420 & later air-cooled KX500 received plenty of criticism too. Suzuki started the new decade with the RM465, it then received a bit of a make over & became the RM500, riders actually liked these two air-cooled machines even though some people said the motors were getting a bit dated & when Suzuki gave their factory riders new water-cooled 500cc bikes to campaign the buying public started to get very excited indeed about the prospect of a production version but it was not to be, Suzuki pulled out of the 500cc market in 85 so this leaves todays vintage racer with little to choose from when considering a big bore Evo Suzuki. Husqvarna finally dumped their air-cooled motors / twinshock set up & produced a water cooled / mono shock bike in 85 but the other major European manufacturer KTM had aced them in 1982 with the fantastic 495, complete with single shock or “Pro-Lever” rear end. KTM steadily improved their big gun all the way through the eighties, in 85 it received a major upgrade & became the 500, each year saw changes until it topped off the decade in 89 with more engine modifications & upside down front forks but I am pretty sure if you dig deep enough, even the mighty KTMs will have chinks in their armour. Maico took the leap into the world of single shock rear suspension, rumour has it that they took a close look at the Honda linkage set up & then tried to copy it but got the geometry / maths wrong, a guy pushing a big maico back to the pits with collapsed rear suspension became a familiar sight at race meetings around the world. Following the success of the twinshock 490, as far as potential buyers were concerned, maico seemed to go from hero to zero over night, especially in the USA. As you may know the company did limp on through the 1980s, at some point they became water cooled & even turned blue but it did seem that the only person in the whole wide world who kept the company flame alight was are very own Mr Bill Brown.

Taking all the above into account our Evo rider in search of a suitable big bore 2-stroke has ended up with a surprisingly small list & the fact that virtually all the bikes produced during the period came with at least one or two problem areas that needed to be smoothed out, will have hit home. Suddenly, the poor old YZ490 that so many people wrote off begins to look no worse a machine than some of the other stuff around at the time. Our Evo rider notices that a good clean YZ seems to cost quite a bit less than the equivalent water cooled KX or CR & maybe the fact of not having to worry about radiators, hoses & a water pump is a bit of a blessing & spare parts do seem easy to find, that’s a plus point also. What about those YZ suspension problems ? tricky one that, but what are the chances of our rider buying any make of bike that has the suspension freshly serviced with spring rates ideal for their weight & riding style ? Answer, No Chance. So because our hero will probably have to sort out the suspension on any make of machine purchased, the problem is not a problem particularly associated with the acquisition of a big YZ. Don`t like the sound of that 4 speed transmission, then buy a later 5 speed model, you even get a front disc brake thrown in for free & the later models do sound better on paper, once set up they should start quite easily for a big 2-stroke & Yamaha did manage to pull some of that power down into the bottom & middle range but what about the vibration ? How long do races last for ? About 15 minuets or so, should a rider be concentrating on the track, picking lines, looking at the rider in front, getting ready to make the pass or should they be concentrating on vibrating handle bars & foot pegs ?  Correct, they are an Evo racer, they should be racing. No, no, no, even though the bikes are not as useless as people have always said I couldn’t live with that “PING” but what’s this, a diagram that suggests with simple modifications to the cylinder head the “PING” can be lessened & make the carb easer to jet as well…..


 As if by magic…. Shortly after publishing this article the following paragraph of text & photo was shared around “Facebook” it regards an advert spotted on ebay USA, it makes very interesting reading indeed…..


” This is a very rare water cooled top end kit for a YZ 490. These were made in France by JPX and the pipe is from V1 in Belgium.The best way to build this is to use a 250 frame and radiators but you could modify a 490 frame. This would use a standard 490 piston although they came with a Wiseco and were available as a big bore also. This kit has the electric water pump and a stator with extra windings plus a rectifier and voltage regulator. Also included is a modified 250 case that will go on a 490 and has a mechanical water pump if you want to go that route. Stephane Peterhansel rode a machine using this type of conversion in a motard racing series during 1991. These don’t show up very often and almost never with the pipes and other little parts. Starting bid $2000 “

YAMAHA YZ490 water cooled kit
Yamaha YZ490 water cooled conversion kit.

The Works… Its always interesting to see what the factory riders had compared to the YZ490 on offer to the general public. By the time the 1970s came to a close Yamaha weren’t doing too bad, factory rider Heikki Mikkola had taken the 500 world championship in both 1977 – 1978  & as the company rolled in to the 1980s, as far as the world 500GP series was concerned it was now the great Hakan Carlqvist in the hot seat. People were always puzzled as to why his big factory YZ500 remained air cooled even when all the other factory bikes had become water pumpers, In fact the company had started to experiment with a liquid cooled bike as early as 80-81, rumour has it that this machine did get a sneaky ride out at a Dutch pre season meeting during the early 80s but then disappeared. People have suggested that Yamaha got a bit preoccupied with developing a water pumper & thus poor old Carla had to ride an air cooled bike that was a bit under developed while he waited for the back room boys to solve various problems with the liquid cooled machine. Physically Carla`s works bike was a big machine, loaded with special one off alloy & magnesium parts, it`s said that when the motor hit the the power band it was an absolute monster, amazingly despite the bike being a bit of an under dog Carlqvist still manage to stay ahead of the superb factory Hondas & take the world championship in 1983. Over the next few years Carla`s works bikes remained air cooled, they had all sorts of exotic parts, oddly shaped exhaust pipes & the motors that became even more brutal, in 86 the factory decided to make the machine even harder to handle by kitting it out with upside down front forks that performed worst than the conventional ones they replaced. In retrospect its a good job that Carlqvist was such a strong & talented rider, those works machines would have finished off a lesser man !


Carlqvist must have helped persuade more people to buy an early YZ490 than anyone else

Against all odds…. While Yamaha were busy trying their very best to kill poor old Carlqvist with the full factory 500cc bike, things were a little different stateside. Broc Glover was given the unenviable task of beating off all the other full factory bikes & riders on what can best be described as a works / production based YZ490. He rode the wheels of the thing & achieved what many thought would be impossible on such a machine by winning the 1985 AMA 500 National title. The biggest change the bike received was the fitting of a 5 speed transmission to replace the standard 4 speeder, work was carried out on the cylinder head combustion chamber & cylinder ports, another exhaust pipe was popped on & apart from slipping a better set of internals into the standard front forks & swapping the rear shock for a better unit, that appears to be it, even the standard carb & ignition system was retained, if what we are told is correct. By using a late model 490 that comes with a 5 speed transmission as standard, can you build your own Broc Glover replica today ? I think you could make something pretty close but whether you will go out & win a national championship is another thing, Mr Glover has what most of us don`t, talent.

At last !! a production water cooled YZ500, or maybe not….. The 1988 YZ model range brochure got every body excited by the possibility of a production YZ500 water pumper, a photo of the fantastic looking YZM500 factory special appeared on one of the pages. The text said that only six had been made & they regarded them as mobile test beds for Yamaha`s new & exciting ideas, the fact that there was no mention at all of these exotic looking machines ever going into production didn’t stop people thinking that they just might. At the time the YZM looked very cutting edge, the liquid cooled motor was housed in a polished alloy frame that incorporated a combined air filter box / sub-frame unit also made from aluminium. The rest of the bike got the same treatment with all sorts of components being made from either magnesium or light weight alloy. For the short time the bike was around it managed to win the 1987 Le Touquet beach race with factory rider Leif Persson at the controls & then Jacky Vimond came back from a serious injury to win the 1988 Swedish 500GP, this turned out to be the bikes only GP victory. Looking at various comments written by people who were lucky enough to actually ride one of these rare machines, it seems that it`s performance on the track never quite matched it`s fabulous looks, one does begin to wonder if a well sorted production CR or KX would have been more than a match for it. The fact that the YZM500 was only around for two years & only six were made will guarantee it`s place in motocross history & I’m sure it will always be regarded by some as the Holy Grail of Yamaha works machines.