Kmx 200 engine in 125

[indo247]

Hi all,
I've just got hold of a KMX 200 engine, and was thinking about putting it in my 125. it looks to me like i could use the KMX 125 bottom end and use the piston, barrel and head from the top end of my spare engine.. which would mean i'd have the 125 engine numbers

Has anyone here ever done this mod? i know i need a new exhaust and re-jet the carb. what about the electrics would it all be the same?

[lukamon]

yep, 125+200 engines had identical internals.

howerver, you need new exhuast, new carb, new inlet rubbers (i think) new ignition coil, piston, rings, and gaskets.
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killa wrote: Im an ass man myself

[MaybeGuy]

make sure you file off the bit that says ''198cc'' on the barrel. otherwise your just asking for trouble.
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Blue_SV650S wrote: it was a sh1te wheelie, but it proves that he can get it up in 3rd and can do angles. In summery, mattsprattuk is a gobby little sh1tebag, dopehead tw4t, but sadly for all of us, he probably isn't THAT full of sh1te!!
Kickstart wrote: Hi I tend to agree with Matt. All the best Keith

[dougon2wheels]

[mad4it028]

[stevo as b4]

The stroke is 54.5mm, the same as the 125. It's the bore which is bigger at 67mm. There is some extra power and torque to be had from the 200cc engine, and a good one can put nearly 95mph on the speedo in good/favourable conditions. It never feels as lively as a Kmx or DT 125 as there is much less of a power band and the engine is quite de-tuned in the port timing and by the exhaust and carb size, compared to the 125, so the extra 6bhp at peak you have as std never feels that much. It does not need tap dancing on the gearlever to find good acceleration and to be able to maintain 60-70mph like the 125 would need. The engine actually pulls well from 2500rpm, and with std gearing it will wheelie off the throttle in 1st and 2nd at 5000rpm. It's more like a DT175MX in it's power delivery than a DTR125 for example.

The carb is the same size, and just needs the jets, needle and slide changing. The gearing is 16/50t instead of 14/48t, and the exhaust is different. AFAIK the CDI is the same or at least has the same timing curve and no rev limit, except for the retarding of the timing at speeds above peak power, which does the same function as a spark cut. The gearbox internal ratio's are different on the 200 engine, but this wont make any difference to it fitting a 125cc bottom end. You need the head as well as the barrel as they are different.

[indo247]

Thanks for all the replys, seems to be a worthy upgrade then i reckon.. 90-95 sounds good to me!!
I just stripped the 200 engine and the barrell and piston are shot, so it looks like not a cheap upgrade!!

anybody know any good places to recoat a nikosil barrel? price ect?
piston kits seem to be easier to come by loads on ebay

[Kickstart]

Hi

For a replate try PJ Engineering in Wolverhampton.

Only other place I know of that actually does replating (rather than just sending it out) is Langcourt Engineering down near Bath, but I don't have their details.

All the best

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

[stevo as b4]

Yeah my first 200 would in still conditions cruise at an indicated 75-80mph without pushing it. You could increase the top speed by 10mph almost by just sitting prone. It would do 80 easily, but an indicated 90mph was full throttle, which says more about the aerodynamics than the power available. The MCN official stats were a tested 93mph top speed, and 15.2sec 1/4m at 88mph.

I always have thought about what would a KMX200 engine be like in a Cagiva Mito. I've never come across a cheap Mito minus an engine, but if i did that would be my thinking!

For Cylinder repair/replating work you could speak to James at BDK engineering. I've had a chat with him as he used to have a KMX200 that was tuned to the hilt. He will be doing my cylinder re-conditioning and tuning work when i get around to sending it to them.

[indo247]

thanks for the info, i have contacted langcourt and they quoted 92.50 plus vat just for a replate, if the barrel is scored or it needs a repair then it is an extra £30 - making £122.50 +vat.

which is not too bad, i just need to source the other parts now
Jet needle 4FL46
main jet 112.5
Piston Kit
Top end gasket set
I have found a BIG ONE down pipe on ebay for 95.00 i already have a BIG ONE end can, will this fit the down pipe to save buying one? also can i keep the 25 pilot jet the one the 125 runs

[Zedxfarin]

I'm working on a KMX 125 right now. Good luck with is project hope all works out. let us know
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Montesa Cota 350cc, Yamaha DTr 125cc, Yamaha Timberwolf 250cc, Yamaha YZ 250cc, Kawaski kmx 125cc, Kawaski kmx 200cc, Yamaha TY80cc, 175cc Chinese Dirt Bike, Chinese Wanyge 125cc, Mini & Midi Moto 50cc - What i have owned.

[stevo as b4]

I've checked and the carb slide is the same, as is the pilot jet. The airbox lid has a bigger inlet on the 200, but you can just cut the plastic open to make it as big as possible on the 125 lid. The 200cc has stonger clutch springs, but if your using the 125 bottom end, id just order yourself a new clutch kit anyway. The exhaust is slightly different between the 125 and 200 and so is the diameter of the stinger. But an aftermarket can should mate up to the 200 front pipe easily enough.

[Kickstart]

[indo247]

Hi, any chance of a pic of the air box cover so i can see the size of the hole?
the bike has had new clutch plates before i bought it, but i don't think the guy changed the springs, because there seems to be some drag and the clutch is adjusted to the max, could a new set of 200 springs do the job and just keep the new clutch plates?

I'm still getting parts together and seems that i'm looking at spending a few hundred quid, so i've been looking around for a kmx 200 field bike that i can cannabalise for the parts, i could probably pick one up for 350 to 400 quid.
here's a pic of the bike at the moment, before i've started

[indo247]

hi, just a quick update. I have got all the bits for my 200 project now, managed to get a complete exhaust and the air box cover from ebay only things i'm having trouble finding is the Jet needle 4FL46 and main jet 112.5 any one got any ideas where i could find these parts?

[Kickstart]

Hi

For the carb jets try Allens Performance.

All the best

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

[indo247]

another quick update. I have all my parts now, got the barrel re-sleeved, new piston kit, 200 air box lid, carb repair kit that i got from NRP carbs and standard exhaust. Still need a tail pipe they are different on the 200, 30mm instead of 28mm on the 125.

only problem at the moment is when i took the KIPS valves out and decoked them, it looks like someone has used the same valve in each side, in the haynes book one valve has like a curved cut out and the other is a square cut out? also in the haynes it says the 200 should have a chamfered tooth? when i look up the port you can see them opening and closing ok, but the one that should be square cut out is obstructing the port slightly? Could i use the 125 Kips valves? i can't seen to find any anywhere.. was thinking maybe lookinf for a valve off a KX, maybe they would be the same?

[stevo as b4]

I don't think i still have my old valves to look at for a comparison. What you will find is that the KMX200's had alloy KIPS valves running in an alloy barrel. The materials design of the valves is far from perfect, but not a total abortion like the Suzuki RGV powervalve set up.

The old style valves used to eventually get carbon'd/ gummed up and then seize in the barrel. The actuation of the valves is by means of a mechanical governor that operates at a pre-set designed rpm. What happens is that the operating rack tries to turn the now seized valves and it can't, so the weak link lets go which was the spindle below the pinion gear. The Valves will probably stick in the closed position, so the top end power will suffer.

Kawasaki re-designed the valves, and the replacement parts listed for on their parts database back in 2000, showed the new valves to look the same, and not like the earlier handed versions. The new style valves are made in steel and do not seize or break due to them being stronger. If ever you do any top end work on the engine, it's essential like all the 2stroke PV engine's to clean and inspect all the PV parts as part of the job. YPVS, KIPS ATAC SAEC etc all need maintainence and have issue's, but treating the valves and related parts as service items will stop serious wear or in some cases *(Suzuki)* engine destruction occuring.

[indo247]

The valves i have in mine are definatly steel, (see the pics) because i soaked them in acid that i use at work it burns off carbon, if you use this acid on alloy it melts it. I also checked with my local kawasaki dealer to see if you can still get replacements, but they no longer produce them. So looks like if they are the wrong ones i'll have to trawl ebay and breakers for them.

I also found out that the old piston in the barrel was out of a KDX 200 and the barrel had been bored out to 66mm instead of 67mm for a kmx, the guy who did the rebore said that they used to put kdx pistons in because they were half the price of kmx ones.

this project is turning into a nightmare, yesterday i put 200 clutch springs in the 125 bottom end and it's made the clutch much stronger, so i'm about ready to strip and put the 200 bits on, i may just try the valves as they are?

[indo247]

job done, bikes up and running as of today. just took it out for a few miles and seems to run ok, it sounds beefy compared to the 125. only thing is the heat it's getting very hot? does anyone know if the 200 has a bigger rad or is it the same as the 125.

now got to run it in, wah 500 miles at 5k

[stevo as b4]

Good to hear you have got it running ok. I think your KIPS valves look like the right type, which should be identical to the 125's really. I would expect that you can still get new PV parts for the 125, as it's not been out of production for that long. The worst issue i have heard about with the 200's is that the 2nd gear set is now NLA, and you can only get them secondhand. This is a similar situation with alot of older 2 stroke's now, as the late 80's and early 90's stuff starts to become rarer.

As for the Rad, well as far as i can see the 125 and 200's have the same size rad, but i found that the 200 would get quite hot in the summer, and it would start to get too hot sat in traffic or doing any slow off road work. This gave them a worse repuation for poor reliablility for serious off road use than the 125's.

For normal road use it should be ok IMO. The cooling system is probably running close to it's limit at 200cc, so there is no spare cooling capacity. Make sure that the thermostat is fitted and ok, and that it opens when it is supposed to. Also i think that running a 70/30 or 60/40 ratio of water to antifreeze helps the cooling system.

Yes the 200 does sound much deeper and more serious than the 125's and it's far less revvy or powerbandy which you either like or hate.

[indo247]

thanks for all your input, very helpful.
I compared the 125 valves to the 200 and they are much smaller, i'm still not entirely sure they are set right, but as i can't find any it will have to do for now?

I will try the 70/30 anti freeze, at the mo it's just got water in it, cos i don't hav any antifreeze, thats maybe why it's getting hot?

i still have the 125 gearing on it 14/48, i have a 16 tooth front sprocket but no 50 tooth back one thats the standard gearing for the 200. what would it be like if i just put the 16/48 on?

also the exhaust is a standard 200 one, was thinking maybe a straight through aftermarket one sometime, what other mods can you do to the 200? i put racing reeds in, but everything else is standard at the mo

[Kickstart]

[BenR]

[Kickstart]