kdx 125 1990

[daddymac79]

looking for info on kdx 125 anything at all
i pickt one up yesterday as a project im not new to bike s and have a crf450r this is just a bit of fun to see what i can get out of it ........ i kno it has a lot in common with kx 125 and that its a resticted version can you tell me if i am right in thinking that it is done by

expantion chamber

exhaust port restricted

wedge in carb

oversized main jet so it runs rich

kips disconected

any info on reversing any of the above would be gr8t or if you kno any diffrent let me kno .....
it is just for fun but i intend getting every hp out of it poss so any tuning ideas would be gr8tfully recived any at all .
i will be porting and polishing but the one thing i dont want to do is start upping the cc ........
so help me if you can ,build the uk quickest kdx125 i will add photos and let you know my progress on the nut and bolt rebuild




i kno its not the best bike
i dont kno why i am doing it
I JUST KNO IM GONNA
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[BigTobyD]

I had one of those in my youth, my favourite early bike by far - getting misty eyed thinking about it! Best of luck!

[CRF_Rider]

the KDX is isn't the restricted version its the enduro/trail model. so it will have different gearing etc.
Id start off at the carb and pipe change them for KX (probably kehin) version. Gently smooth out out the inlet and exhaust ports this usually adds a couple of hp too (the diameter isn't the issue its the smoothness). I wouldn't want it running too rich as you will be going through plugs faster than you know. Quick action (1/4 turn) throttle. Polish the top of the piston head too.
I would also think about putting a 185 conversion on if ya can. I've had a go on a YZ185 and its a great improvement.
Is it premix or auto lube?
I'd be trying to save as much weight as possible so converting it to premix, taking off all the lights and running it as good visibility only MOT, taking off the battery and just using the kicker etc etc
Also try getting a second hand KX ECU i think that should help out with the fueling and the rev limiter.
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Why is it everything i race, seems to be going backwards?
Current: Honda CRF 450 R Supermotard
Previous: Yam TY250 x2, Gas Gas TXT 200, Sherco 290, Suzuki TS 50,Honda CG 125, Yam SR250, Suzuki DR-Z400E, Yamaha YZF R6 112rwbhp

[stevo as b4]

I don't know if they are restricted much differently to the KMX, but it will most definately have a restricted front pipe, so that should be modified or changed to a high performance non road legal version. The KDX engine seems to have alot more in common with later KX125 engine's in terms of the design, and it may well be possible to fit the KX exhaust, and carb which would need alot of re-jetting to even get close to working well.

I doubt that any of the late model KX cylinder's would fit onto the KDX crank cases, but i don't know for certain. It might be that an early 90/91 KX engine would be similar enough for parts to be able to be changed between them. The KDX has the same reedblock size as the KMX and KDX200/220, so id think about a V-force reed cage and then a bigger carb than std to match the other engine tuning your intending on. The std KDX carb is a Keihin PWK28, but the KDX220 runs a PKW33, and that is probably more than big enough to work on a tuned KDX125 engine.

If your doing cylinder porting and re-machining the head/squish area, then id suggest you don't touch anything yourself unless you are an experience two stroke tuner. It would be far better and give much better performance if you send the barrel and head off to a professional 2stroke tuning firm that has years of experience in modifying engines successfully for greater performance. There is nothing wrong with using a small less well known tuner, if they have an excellent reputation and come highly reccomended.

[daddymac79]

its all good info, after striping it down yesterday i found that the autolube was not used and the electrics were all choped no battery or lights but i think i will be puting these back on ! against advise i know...... the head is now off and it looks as tho it needs re plating any idea on cost any one ? the port work i will carry out myself i have ported superchargers and such before and feel confidant in what i can acheve.... and one more thing i need to ask is how do i chose the right piston -ring size without knowing what was last installed by this i mean i take it that the bore wares and the ring size changes or i might be off the mark ... and just to add could i slit the exhaust and remove any restriction and reweld if anyone has done this before some advise would be gr8tfull

a big thanks to everyone for your info
and just to add i am sorry for the spelling mistakes but i am dyslexic and i havnt downloaded the spell check yet

why do they use a word like dyslexic i.e a hard to spell word to describe someone who cant spell?
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[SusanBoyle]

Hi, I've just brought an kdx125 1994. I need to get a new rubber gasket which goes on carb. Also i would like to tune it. I would like to buy a kx125 gasket and carb but does anyone know which year should i buy?

[weasley]

I have a 96 French market model (not that they really changed at all over the early 90s). I can tell you after mine caught a ring in the inlet port that replacement engines and/or barrels are nigh on impossible to find and are not shared with anything else. The big difference with the 125 is that the carbs sit on the crankcase and it is crank-inducted, rather than straight into the barrel. The KIPS system is present and working.

I have a Kawasaki workshop manual so planning to give it a good once over as I rebuild the engine with the rather expensive s/h barrel I did finally find. I'll probably get the old one bored and sleeved, so it can be reused in future and no need for replating.