KMX 125/200 OVERHEATING

[elf69]

Hi i have recently bought a rather old kmx 125, although I was told it has a 200 engine. The problem I have found is that when i take it green laneing it overheats

Is there a modification or a different rad that i could fit to prevent this? - like a kdx one.
Any ideas would be greatly recieved.
thanks
Kev

[Kickstart]

Hi

Not sure on mods (does the 200 have a larger radiator?). However worth checking the radiator is in good condition first, possibly having a session with tweezers straightening all the fins.

All the best

Keith
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[elf69]

Thanks Keith, think the rad is standard 125
probably could do with a bit of straightening

[stevo as b4]

Make sure that the stat is fitted and working correctly first. On off road KMX's and field bikes, the stat is often removed causing more problems than it solves.

The KMX200 rad AFAIK is exactly the same as the 125's, and TBH the 200 has a fairly marginal cooling system for off road use too. They have a reputation for being less reliable due to overheating than the 125, caused by the fact that in constant slow speed and off road work, the 200 cannot get rid of enough heat quickly enough. For open road use it's fine and for a bit of town riding, providing that the cooling system is all in good condition.

It sounds like your rad is not in ideal condition, and most battered off road bikes, will have bent and damaged fins after years of use. The 200 will not cope with continuous slow speed town riding, and heavy off road work in hot weather conditions IMO.

People have fitted fans with a manual bar mounted switch to help with this problem, and im told that it does work if a suitable set up is used. On the 200 that im building, im going to replace the std Steel rad, with a custom built alloy one which should be around 30-40% more efficiant, and cool better without needing to try getting a bigger rad to fit, or a dual rad set up, which is more complex.

The KMX200 unlike the TS200R and DT200R has a single rad, but you won't find many 200cc bikes derived from a 125 engine design, that use a single rad, due to the fact that the bigger engine capacity needs more cooling ability.

[elf69]

Thanks Steve great reply some good food for thought
many thanks

[jakeus]

Hi,great advice from Stevo there!.any1 know if the kmx200 engine goes straight into a 125?. Without needing to change anything else,ie;CDI UNIT,IG COIL, ECT.I'm no mechanic but mechanicly minded!, have built an awsome kmx from scratch & just swapped a perfect 125 engine for a not so good 200 only to be told by a mechanic m8 that he THINKS i need to change some other stuff & maybe even the loom???? Any feedback greatfully recived. many thanks Jake
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jakeus

[stevo as b4]

Hi, well first thing is get some pics of this nice KMX project you have up!

The 200cc engine is best used in it's entirety, and not with the 200cc top end fitted to a 125cc bottom end, which does work and fit, but there are lots of small differences. Assuming you have a 200cc complete engine then this is what is different to the 125.

1, CDI unit (AFAIK the timing retard is different on the 200's)
2, The expansion chamber and silencer is different (bigger on the 200)
3, The Carb is the same but the main jet, and jet needle are different. MJ is 112.5, and the needle is 4FL46
4, The final drive is 16/50T on the 200.
5, The airbox lid has a bigger inlet on the 200.

That i think is it, apart from the changes to the engine it'self such as the oil pump delivery quantity, primary drive ratio, and internal gearbox ratios. The 200 has an extra clutch plate as well.
The radiator as said is the same.

If your engine is running like crap with the correct carb settings and the right exhaust, then check all the normal stuff like ignition, (no timing adjustment can be carried out), and check the reeds are seating ok etc etc.

The compression pressure for the 200's should be within the 110-175psi range if the engine is any good.

[jakeus]

Hi,thanks for the quick response,i do have the complete 200 although its going to take a few quid & time to get up to scratch!.I have a new complete bigone(fresco)pipe,a k&n TYPE filter(cheap£25)& carbon reeds+the 200 came with the 2-stroke pump.So i guess Stevo?,all i need to do is change the main jet& needle,buy a 200 cdi unit?. Also i have heard that a kdx v-force reed block fill fit?.Sounds interesting!. Will try to add some pics now . Basiclly i powder coated the frame & swing arm(black).Got a old(91)set of kx125 usd forks (wp i think?).Supermoto front fender.Vapor trailtech digi clocks(v cool ).Rage streetfighter headlight.Led tail light.Wavy f-disk.Avon gripster tyres at the mo.....but i have seen a kmx on youtube with gsx750f wheels& tyres that i will be fitting ASAP !!! Then fit nobblys to the other wheels for a quick sm/enduro swith over .THANKS STEVO.Your expert opinion is much appreciated. PS; Let me know if pics don't go up???? [img][/img][img][/img]
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jakeus

[stevo as b4]

I wouldn't mind seeing some pics of the KX usd front end, and info on what you had to do to fit it. Did you manage to press a new stem into the KX fork yokes or was there modification to the yokes and or headstock needed?

I think with the 200 CDI box and carb settings, it should all work ok, if the engine is in good condition. It's well worth compression testing it to get an idea of how healthy it is too.

The KDX 200/220 reedblock will fit the KMX 125/200, as the reed cage housing/casting is the same size and has the same bolt spacing. There is as you rightly say a V-force reed cage available for the KDX's, and that is a mod im going to incorperate into my KMX engine build. The KDX inlet rubber/manifold will accept the Keihin PWK33 or 35mm carbs, and the original KMX manifold will accept a Mikuni TM28 or TM30SS carb. The later is a mild upgrade for the 200's, but works great on tuned 125's! On alot of KDX's there is not an oil injector nipple fitted on the inlet manifold, but IMO the best way to add one is to get the carb body carefully drilled and have the injector nipple pressed into the carb itself.

I'd like to see a pic of the GSX750 wheels fitted to a KMX, although i imagine that they are quite heavy, compared to some custom build SM wheels even when retaining the stock hubs!

Something i am fairly certain of, but i havent tried it yet, is the possibility of fitting a 300mm KLE500 front disc to the KMX200 hub. It seems like it's the same hub as far as i can tell, so it hopefully bolts straight on, for a big disc solution for SM builds.

[Blue_SV650S]

How do you know it is overheating (no temp gauge right?)
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The purpose of life is to fight maturity.

[jakeus]

Hi, i'll email my email....reply & i can mail you some pics back.tryed uploading on here but said no more than 1 meg?.I basically got a complete kx front end,yoke,legs,wheel,brake system...The kx yoke stem is a bit longer & tapers at the bottom.My frame is an old one so i replaced the [ball&cup] headset bearings with a new kmx tapered roller bearing set.They fit great untill the bottom one hits the tapered yoke stem at the base.So i took the yoke & bearing to a local machinist who made a special tool for his lathe to take off about 2mm at the base of the yoke stem.Cost £40ist time & £20 the second as he kept the tool.As the stem is also too long i used the old cup from the old head set bearings as a spacer,sat the bottom bearing on that & everything tightened up in the frame neck ok(any spacer could be used) .Rides pretty good but haven't tested it properly yet as the forks need a rebuild,jacks the front up a bit so more ground clearance!.A great mod i think as the original forks are a definite week point.Used the kx caliper with the kmx master cylinder & ss goodrich braided line.Could easy take some kx talon/excel sm rims now.as you say the gsx wheels could add a bit to much weight?.Did look very cool though!. Check out youtube...(my kmx 1 in a million)that's where i saw the gsx idea,i'm sure the rear fits straight on?. I also recon this front end mod opens up more upgrades such as high end sm or mx forks,yokes,like bud racing & such like+the brembo supermoto brake systems .The one on youtube with the gsx wheels also has ktm 250 usd's & looks pretty sick!. Really am greatfull for your help & interest,will mail some pics asap,thanks again Jake PS;May join youtube just to make a vid & post it on there?.will put the link on here if i do.
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jakeus

[jakeus]

blue-sv650s......The trailtech vapor digi speedo has a sensor that you fit into your rad hose& picks up the engine temp .can set an orange light for warning that turns red when critical.
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jakeus

[Blue_SV650S]

[jakeus]

,,,,,,,,,Also have 3 led numberplate bolts as warning lights,blue for full beam,green for neutral & red for 2stroke res level.As i said the vapor clocks do the engine temp
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jakeus

[jakeus]

the vapor is pretty good with a precise readout,average temp is about 150/160f ,warning set for 180f & criticle set for 190f i think(got bike shop to fit it !).that was with the 125engine & have to get the 200 up to scratch but will let you know.cheers
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jakeus

[Blue_SV650S]

eh?

so you have no physical signs of overheating and you have not tested the only thing that is making you think you have an over heating problem to start with

besides, if it is running at ~155F ... that is ~68C, which is a fairly healthy temp for a 2t!!!!

I am really struggling to see you have an over heating problem at all to be honest. ... what makes you think you do?
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The purpose of life is to fight maturity.

[Kickstart]

Hi

For comparison the RS125 stat doesn't open until 65 degrees (150 fahrenheit), and I wouldn't be even slightly concerned at 80 degrees (176 fahrenheit).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[jakeus]

blue- hi,im not asking about the overheating prob.dont have 1 yet!.was getting stevo's advice about putting a 200engine into a kmx125 cheers
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jakeus

[Blue_SV650S]

[jakeus]

Hi stevo,have just got the carb jets and cdi unit thanks to you!.Regretably the 200 engine is a non runner & needs a lot of tlc so wont be running anytime soon.A good chance for a proper overhaul though.Have joined youtube & posted a vid of my bike so you can have a look if you like?.It comes under "kmx,custom built from scratch".Hope you like it
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jakeus

[stevo as b4]

Hi mate,

I've just seen the youtube vid, it looks quite impressive having a usd front end on the KMX. Maybe you can take some more pics of the yokes and if you have any pics of the work you had to do to change the steering stem or machining to fit the KX forks to the KMX headstock. Was your usd front end from a 125 or a 250KX, and does it raise the front of the bike much over std?

As for your engine, well im glad you've managed to locate a 200cc lump, as they are quite hard to get hold of now, (not as hard to find as an MTX200 engine though!). They can often be pricey too, and the last secondhand KMX200 i bid on on ebay, went over £100, which is way too much IMO for a secondhand unknown history engine that could need a full re-build.

If your stripping your 200cc engine down, then the most important thing to check is the gearbox really, as i think individual gear sets for the KMX200 are now NLA new. The crank may be ok, but obviously check it out, and it's wise on the 200 to change the main bearings along with the crank oil seals, as they do wear quicker tbh!

The most expensive part of a KMX re-build will be if there is any damage to the Nicasil bore? If it looks ok, then just order a new OEM or decent quality pattern piston and ring kit, with all new gaskets, circlips and small bearing etc. I think the 200cc engine would run with a 125 CDI, but i have heard that it's different so it's best to fit a 200cc unit to be safe. You will need a 200 expansion chamber, or an aftermarket 200 one, as they are different to the 125's.

A decent std 200 will have around 26bhp at the back wheel, and my first 200 would do an indicated 90mph without too much trouble. A tuned one should go off the clock on std gearing, but 90mph+ on a small light trail bike is not a great place to be really.

If your tuning the 200 engine, the i'm told the best first mods are an aftermarket exhaust silencer, (the KMX silencer is fairly restrictive on a 200), and then a bigger carb. The TM28 Mikuni and TM30SS both fit on to the std inlet manifold, and airbox rubber pipe.
A 33 or 35mm KDX/KX carb will need a KDX inlet manifold to allow it to fit, without alot of hassle.

[jakeus]

hi stevo

will make another vid explaining how i got the yoke to fit asap.it does raise the front end a bit but not to much...i like it ,but i am 6ft!.

as for the engine.....not good
clutch gone,metal fillings in right hand casing(from kips rod mechanism)white gunk for oil(water in there at some point),black crud in left casing/flywheel(crank seal i guess???)All in all a lot of work for a already very expensive engine(ebay£240) .Bore & piston ok though .....do i have to split the casings to change the crank seals/bearings m8???


Looks like i need a new expansion chamber as well as like you say the 200 outlet is bigger than the 125's...gutted,more money.

i have a modified yoke spare if you want to buy it?,as well as the forks,brakes,wheel& disk.... but the forks are slightly bent i think?.thats why i bought a whole new front end for a second time
just a thought,let me know if interested?. will show them in next vid


just waiting for clutch parts & ill start the rebuild,wish me luck i need it !

as i said new vid asap with proper walk-around & front end explained.first one was a bit crap as i wasn't sure if i could upload it,so was a trial run really!.Have loads of pics of build as well so mail me if you like (jake_milford09@hotmail.com)

cheers
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jakeus

[jakeus]

vid posted on youtube stevo! kmx usd conversion
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jakeus

[raniel]

Please help I'm not a mechanic but I love my KMX

My KMX changes idling or even dying when I rev up.

Conditions:
Air filter is clean
Gas is full
New spark plug
there is current (so I assume CDI is working fine)
2T is full and seems working
with smoke
Carb newly tuned

Thank you very much

[dangerousdave]

low compression
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1988 Kawasaki KMX 200

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