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HardDriver |
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 HardDriver Nova Slayer
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stevo as b4 |
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 stevo as b4 World Chat Champion
Joined: 17 Jul 2003 Karma :   
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 Posted: 20:11 - 04 Aug 2014 Post subject: |
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A lot of questions!
Firstly the newest KMX125's are from 2002, maybe a few sold into 2003. They are a comparable 125cc 2stroke trail bike with the likes of the excellent DT125R and the rare Suzuki TS125R. They would really not be much different on the road to even an Aprilia RX125 or Husqvarna WRE125, but newer more competition orientated bikes like these are better off road with a stronger chassis, better quality longer travel suspension etc.
My first advice with buying any 125cc trail bike is buy on condition not model. Also if you want a clean tidy bike with good plastics and cosmetics, get the best you can find, as replacement plastics/panels are often expensive and hard to find for 2stroke 125's that have been out of production 10years or more.
The KMX is a fairly robust reliable bike, with a decent engine that is not too demanding of maintenance, and is similar to the other Japanese 125's in that respect. I'd be expecting the motor to go around 10-15'000miles between top end re-builds depending on how you treat it. Restricted power is 9KW, and un-restricted is 18KW. De-restriction is a simple process compared to 20003> DT125R's etc.
Top speed on std gearing is 80mph, but if used on the road only a 15t front sprocket is a good mod to drop the revs and gain 4-5mph top speed, and make the gears a touch longer too.
The suspension on the later ones has a damping adjustment on the rear shock, and the std suspension is ok for trail riding, or playing around in woods or fields. It's not really up to being blasted around MX tracks, the KDX125 would be better for more serious off road use, or a KTM, or Husqvarna enduro derived bike.
40mpg is about the average fuel consumption. You'd be lucky to get more than 45mpg at best.
There's not many common faults or problems specific to KMX's, but things like checking the alloy wheel rims for corrosion is important. The sidestand cut out switch can play up, but it can be removed easily. The KIPS powervalve is generally reliable, but can fail if it gets too gunged up with carbon. If it does fail, it's usually snapped spindles on the valves themselves, but failure won't cause engine damage like the Suzuki ATEC system.
Part availability is good mechanically, but plastics and cosmetic parts are getting harder to find, and new bits are expensive. Like the DT125R thousands of KMX's were sold over a span of 16-20years, so second hand parts are never far away on Ebay etc.
Good KMX's are maybe starting to go up in price, as 2stroke 125's are getting a bit rare these days and a nice one is hard to find now. Project bikes should cost £400-1000 maximum, and a tidy one £200-400 more maybe.
Performance wise the bike was tested at 0-400m in 16.6sec@76.2mph. I'd expect the 0-100kmh time to be around 8seconds in 18KW form.
The only really important thing to check when buying one, is to make sure it's a legit bike and has not been stolen. A lot of KMX's and DT125R's etc will have been, and making sure you have the correct frame number's, log book and keys is very important.
After that it comes down to condition and how it's been looked after, along with how nice you want it cosmetically? Any tatty bike will cost a lot more to make look smart, than buying a tidy one with clean not scuffed and matched panels etc. Avoid anything that's been used as a field bike and has no electrics fitted unless you want a lot of work.
Also expect any hard used example to have worn out suspension by now, the rear shock on many will be scrap, and the Uni track linkage bearings wear out and seize on neglected bikes. New bearings and seals to re-build the rear end are over £120.
Lastly buy on condition, and not the model. The KMX, MTX, TS125R DT125R etc etc are all pretty similar in spec and performance, so which you get makes little odds really, but a nice example of any will still be a good fun bike! |
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HardDriver |
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 HardDriver Nova Slayer
Joined: 26 Feb 2014 Karma :     
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 Posted: 08:11 - 05 Aug 2014 Post subject: |
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Hey, really thanks for your long post about this bike. Now, I know more about it. But I have some questions about some parts in the texts, because I can't really understand what does that mean .
1. Aprillia rx 125 or husqwarna wre 125 suspension in road will be practical as dt, kmx ant that type bikes, but in offroad wre and rx will be better?
2. Is it true, what kmx in de-restricted status can broke a lot and engine is not reliable at all?
3. If you want to de-restric, what should I do to dot that?
4. to go around 10-15'000miles between top end re-builds depending on how you treat it. You mean, when you change pistons, rings, finger, cylinder? Is kmx cylinder is made of aluminum? Is it true, that 2 stroke bikes (whic depend on kms or miles) acceleration is getting slower and slower, you get power less and less?
5. What do you mean damping adjustion on the rear shock? Later ones, 1999, 1997, 2000 don't have it? Also, if I ride on mx tracks I just fell not comfortable or I will be killing my suspension ?
6. Okey, now the hardest part, the sidestand cut out switch can play up, but it can be removed easily. I don't get what you mean. Could you explain more?
7. Too gunged up with carbon? That means powervalve getting polute by carbon and other materials (which come from engine work). How do you stop that? Is that affecting aceleration or power? Maybe need to ride slower to stop that.
8. Snapped spindles on the valves themselves? 2t stroke have valves? What does that mean "snapped spindles"? It just kips clean by himself? Don't need to do anything? It's really confusing . In dt it's just powervalve, I think a bit simpler.
9. Uni track linkage bearings. Is that front fork or rear shock you talking? How to know, that suspension is dead? Because I think I'm gonna buy 1997 or 1999, so what is really good stuff. Need to know more about that uni track and those linkage bearings, also seals.
Thanks, also, maybe you know who have service manual, I want to watch a bit . REALLY THANKS. I can't believed how one man knows so much . You like some kinda motorcycle wisard. |
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dangerousdave |
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 dangerousdave Traffic Copper

Joined: 22 Apr 2011 Karma :   
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 Posted: 11:53 - 05 Aug 2014 Post subject: |
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HardDriver wrote: |
You like some kinda motorcycle wisard. |
haha yes stevo as b4, it doesn't matter what you ask him about KMX he will always have an answer !
Here's my 5 pence worth:
1. Aprillia rx 125 or husqwarna wre 125 suspension in road will be practical as dt, kmx ant that type bikes, but in offroad wre and rx will be better?
These two bikes are less practical than the KMX in my opinion. The engines of RX125 and WRE125 need more attention than the KMX125.
Offroad, the WRE125 will be the best as it has much better suspension.
The RX125 and KMX125 will be simular off-road, as the suspension is of the simular type and design.
2. Is it true, what kmx in de-restricted status can broke a lot and engine is not reliable at all?
I would not say this is true, as long as they are properly maintained. Poorly maintained and abused engines can be damaged, the same as any other two-stroke engine.
3. If you want to de-restric, what should I do to dot that?
Easily, there are plenty of detailed instructions about on the internet. Most bikes are derestricted now anyway.
4. to go around 10-15'000miles between top end re-builds depending on how you treat it. You mean, when you change pistons, rings, finger, cylinder? Is kmx cylinder is made of aluminum? Is it true, that 2 stroke bikes (whic depend on kms or miles) acceleration is getting slower and slower, you get power less and less?
Yes, 10-15,000 miles is easily achievable after an engine rebuild. Usually just replacing the piston is fine, unless there is any other damage.
Yes KMX cylinder is made of Nikasil. It is a very hard type of coating, which is resistant to wear.
No, they do not get slower with age if the engine is rebuilt at regular intervals.
5. What do you mean damping adjustion on the rear shock? Later ones, 1999, 1997, 2000 don't have it? Also, if I ride on mx tracks I just fell not comfortable or I will be killing my suspension Very Happy?
Yes, all later bikes have damping adjuster in rear shock. I think it is 1986-1990 which do not have.
KMX are not really suited to motocross tracks which we have here in the UK. If you want to ride motocross then buy a motocross bike, they are very different.
6. Okey, now the hardest part, the sidestand cut out switch can play up, but it can be removed easily. I don't get what you mean. Could you explain more?
Can't comment on this as my bike does not have the sidestand cut out switch.
7. Too gunged up with carbon? That means powervalve getting polute by carbon and other materials (which come from engine work). How do you stop that? Is that affecting aceleration or power? Maybe need to ride slower to stop that.
To stop that, you need to dissasemble the powervalve every 10,000 miles, clean it, and put it back together. It is not a hard job. This is the same with most 2-stroke bikes with a power valve.
8. Snapped spindles on the valves themselves? 2t stroke have valves? What does that mean "snapped spindles"? It just kips clean by himself? Don't need to do anything? It's really confusing Very Happy. In dt it's just powervalve, I think a bit simpler.
If you clean your powervalve as described above, you will not have "snapped spindles" so you will not have to worry about this.
9. Uni track linkage bearings. Is that front fork or rear shock you talking? How to know, that suspension is dead? Because I think I'm gonna buy 1997 or 1999, so what is really good stuff. Need to know more about that uni track and those linkage bearings, also seals.
Uni-track is rear suspension. You will know if suspension is dead because it will ride like a bag of sh*t.
Dont buy a bike which rides like a pogo stick or rocking horse as it will cost you a lot of moneys. ____________________ 1988 Kawasaki KMX 200
Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50 |
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Boxing |
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 Boxing World Chat Champion
Joined: 13 Mar 2012 Karma :   
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 Posted: 12:50 - 05 Aug 2014 Post subject: |
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The KDX is a faster model. The engine is supposedly a KX 125 engine, with a different barrel. So I read on a forum anyway, maybe someone could confirm if this is true or not?  |
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HardDriver |
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 HardDriver Nova Slayer
Joined: 26 Feb 2014 Karma :     
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 Posted: 18:48 - 05 Aug 2014 Post subject: |
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I get it, thanks for your help. But still, have some questions.
Then you reach 10-15 thousands miles, what happens to the bike? It just get slower and less powerful? Engine is hard to start? Why do we need to do re-builds?
Also, what is what sidestand cut out and so one, I don't understand what is that? Don't know who mean that words? Could explain in simple words?
Also, how much kawasaki kmx 125 should be "okey" to ride, not to killing bike, (km/h)? How much? Also, what happens when powervalve just become filty with all these carbons?
Also, what gear oil and motor oil should I put, bike is 1997, maybe full synthetic, but is not cheap.
Also, I try to explain as far as I can. So, when you put 1st gear from neutral, don't exemt the clutch, don't get bike, just make 1st gear and so, bike's engine got off? Whats wrong with clutch or bike? Is this normal think? ALSO PLEASE, WHO HAVE MANUAL SERVICE FOR KAWASAKI KMX 125 or KNOW WHO HAVE PLEASE SHARE, I WOULD BE REALLY REALLY GRATEFUL.
Also, it's true, that if your battery is not dead, but kinda bad, in kmw 125 lights are bad (light is small and so one), what about generation, shouldn't generator give a light enough power, not just a battery? |
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dangerousdave |
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 dangerousdave Traffic Copper

Joined: 22 Apr 2011 Karma :   
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 Posted: 20:38 - 05 Aug 2014 Post subject: |
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A rebuild is good at 10-15, 000 miles, as they often have wear to the piston and cylinder at these miles.
There may be a rattle from the engine, this is a sign that a rebuild is needed
What happens to the engine at 10-15k? It may loose some power, yes. It may be rattling or making other noises.
However if the bike is ridden hard, it may rattle and loose power after 4,000 miles or less. ____________________ 1988 Kawasaki KMX 200
Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50 |
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stevo as b4 |
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 stevo as b4 World Chat Champion
Joined: 17 Jul 2003 Karma :   
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 Posted: 00:04 - 06 Aug 2014 Post subject: |
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Boxing wrote: | The KDX is a faster model. The engine is supposedly a KX 125 engine, with a different barrel. So I read on a forum anyway, maybe someone could confirm if this is true or not?  |
From what I've seen of the engine close up, it looks to be based on the 1988/89 KX125, which is the first year that the KX used crankcase reed induction. The KIPS valves are different and fitted differently in the cylinder, but they work the same way as those on the KMX. The carb is a PE28mm Keihin on the KDX, but they are supposed to be 24.5bhp in full power form, so only 0.5bhp more than the KMX.
They KDX has a stronger duplex perimeter frame, and longer travel suspension, only the very early ones had rwu forks, then they fitted USD forks, again aping the KX125 design of the time.
The KDX is however about 10kg more than the KMX, and in restricted 12bhp form, it's at least 6-7mph slower, barely managing 60mph. I don't think the 0.5bhp extra in full power form would make it any quicker than a KMX, but it has a better chassis for off road use.
I'm sure that with a bit of preparation, the KDX125 would be a decent beginner's enduro bike, and not far behind KTM's and Husqvarna's of the time. |
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HardDriver |
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 HardDriver Nova Slayer
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dangerousdave |
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 dangerousdave Traffic Copper

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 Posted: 12:35 - 06 Aug 2014 Post subject: |
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HardDriver wrote: | stevo, hi, could you answer my other questios. I would be really grateful. Thanks. |
Sidestand cutout is a switch which does not allow the engine to run when the stand is down. This is for safety, so learner riders do not ride away with the stand down and cause an accident.
These switches can fail, causing the engine to not run. If this is the case, the switch can be replaced. Not a big deal. It is a common problem on trail bikes due to mud and water from off-road riding.
Regarding the power-valves. They need regular cleaning. It is the same with any bike with power-valves. If they are not cleaned and maintained, the valve becomes "stuck" in one position. This means the bike will become less powerful usually. There is the chance of damage to the valves themselves if they jam totally.
If this happens you'll need to take the power-valves apart, clean and inspect them for damage, and replace the broken parts. This can be expensive. So, clean your power-valves regularly and there will be no problem.
Put gearbox oil in a gearbox. Like Silkolene Light Gear Oil.
I'm not sure what you're getting at with "putting bike into gear"
And "don't exempt the clutch", and "don't get bike". It's not making much sense?
For a manual, why don't you buy one off eBay?
If battery is dead then replace battery. Not good running without working battery anyway. You will find lights are better. ____________________ 1988 Kawasaki KMX 200
Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50 |
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HardDriver |
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dangerousdave |
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HardDriver |
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HardDriver |
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stevo as b4 |
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 stevo as b4 World Chat Champion
Joined: 17 Jul 2003 Karma :   
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 Posted: 16:43 - 09 Aug 2014 Post subject: |
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The info you need is easily found TBH.
https://www.bikechatforums.com/viewtopic.php?t=293265
Engine oil for any liquid cooled modern stroke should really be a fully synthetic 2stroke oil of a non pre-mix only type if your running autolube? If pre-mix then it does not matter on which kind of oil you use, but a thick pre-mix only oil will not flow well enough to work in an autolube system.
Are you dead set on a KMX by the way?
There is still a fair choice of secondhand 2stroke 125's in good condition, but with them all being less common now, I really would buy whichever one was cleanest in the style of bike you want?
In other European countries things may be different, but in mainland Europe there is plenty of bikes around, and in some countries like Italy, you will still find quite a few decent home market bikes, which would be just as good as anything else, spare parts allowing? |
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HardDriver |
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 HardDriver Nova Slayer
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dangerousdave |
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HardDriver |
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dangerousdave |
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 dangerousdave Traffic Copper

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 Posted: 08:57 - 10 Aug 2014 Post subject: |
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HardDriver wrote: | Oh, I get it. With choke should need gas or not? Also, is it bad to start engine without choke? And what about battery and clutch, really no one know? Or I don't now how to say correctly? |
With choke, you don't usually need "gas"
Your problem with battery and clutch I don't understand? ____________________ 1988 Kawasaki KMX 200
Previous: Yamaha YZF1000, ZZR600, KMX200, DT50, KX80, CG125, PF50 |
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HardDriver |
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HardDriver |
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 HardDriver Nova Slayer
Joined: 26 Feb 2014 Karma :     
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 Posted: 14:27 - 16 Aug 2014 Post subject: |
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Hi, I want to know more, how to know when your bike is enough warmed to drive in high rpms and so one? How to know? When I'm start the engine, i'm like 2-3 minutes don't ride, when ride in little rpm, but maybe it's to much warming .
Also, stevo b4 said, that for modern bikes need fully synthetic, but what about my kmx? it have 1992 year engine, it's still modern ? But I must say, that the engine is in pretty good condition, piston and so one is like new. So I don't want to harm my bike, what should I do?
Also, when need to use choke? Because I don't know it's really working in my bike. It's really confusing in kmx, maybe it's broken.
I'm talking about kmx 125 |
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_Iain_ |
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HardDriver |
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 HardDriver Nova Slayer
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 Posted: 15:50 - 16 Aug 2014 Post subject: |
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_Iain_ wrote: | HardDriver wrote: | Also, when need to use choke? Because I don't know it's really working in my bike. |
If it starts without it, you diddn't need it.
If it doesn't start without it, you need it on.
CR usually fires up fine without choke. Only needs it when it's very cold, or pissing it down with rain. Try and ride with it on, and it splutters, coughs, and then fouls the plug up and won't restart till plug replaced/cleaned. |
Yes, also, I read a little bit manual, it's talking about torque when you want to screw somebody. Also if you want choke cable or clutch cable to lubricate, need some kinda pressure lubricate? Can I use just normal oil? But in winter, there is cold, that simple oil just freeze? So what should I do?
Also about motor oil. I think I will use fully synthetic, not to good oil for bike ? That's one of the importest questions in 2 stroke - when your engine is enough warm? Can someomone tell my answers. |
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Old Thread Alert!
The last post was made 11 years, 59 days ago. Instead of replying here, would creating a new thread be more useful? |
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