KMX 125 revs to 5k, dies

[Rafe Dent]

Hi, new to this forum.

Just got Kawasaki KMX 125 from year 2000 approx. Been standing for a year or so, though. Converting to use in the woods with kids PW80's etc.

Came without carb and cut cables, so found standard s/h Mikuni 28 VM. Stuck it all on (and off, and back on several times), as per handbook - checked cable play for carb and oil pump (and for body sitting on carb bed, throttle off), set screw at 1 and half turns, and idle screw at just lifting body - fired up to my amazement.

Starts fine on choke, throttle closed. Then revs to 5k and if taken beyond sort of splurges and dies, feeling very 'chokey'.

Can ride it up and down drive to 5k, anything beyond go into nightmare cut-out scenario. Battery dead, but otherwise not too bad shape.

Any ideas? Thanks in advance, Rafe.

PS Pop in if anyone wants stop-off in Frech Alps. Annecy 15 mins, Geneva 45.[/img]
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Kawasaki 125 KMX - woods & tracks only

[stevo as b4]

It sounds most likely to be a jetting problem and that the mixture at higher revs is too weak or rich. The std carb for a KMX125 is:
Mikuni VM26SS
Main Jet:102.5
Pilot Jet: 25
Needle Jet: O-4
Jet Needle: 4FL44
Needle Position: 2nd from top
Float height 21mm +/- 2mm

Make sure all the carb settings are correct, and that the exhaust and airbox are correctly fitted. I would think that the cause of your problem is very unlikely to be the CDI unit, but if it still is no better once you have gone over the fuel system and corrected any issues, then it's probably the next thing id try and change.

[ms51ves3]

Too much air. Upjet.

[Rafe Dent]

Thanks for all that. Excellent.

I'm sure you're right. Have you by any chance got a photo of that jet?

Called in at the bike shop and he had a jet, but it had a sort of extended hexagonal nut on the bottom (about 2cm long), which he said wouldn't work. Mine is more like 1cm, with normal screw bottom. Also, does the needle jet just push out (for cleaning)?

I also got an in-line fuel filter, coz I was a twit and didn't swill out the old tank before fitting, and I imagine thats full of bits and pieces which'll be tricky to get out now (bike been stood for a couple of years).

Found this great post which taught me loads about carbs overnight, for any other bike newbie out there (that allowed eds?) https://forums.somethingawful.com/showthread.php?threadid=3017242&userid=0&perpage=40&pagenumber=1

Will let you know how I get on, not too sure I'll be able to attack it 'till the weekend.
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Kawasaki 125 KMX - woods & tracks only

[ben350]

I dont know much about KMX's as I have never worked on one.

The needle jet or emulsion tube as its sometimes also called is held in by the main jet. Remove the jet and the brass washer underneath it, then put just the jet back in as this will give you something to hit (gently) with a mallet, the emulsion tube will then pop up into the carb body - you will need to have the slide removed for this

My DTR runs a 28mm Mikuni flatslide and that has a 210 main jet in it as standard - not sure if this is any help but it may help get an idea what kind of size you need

Also if you get tempted to run pre-mix not auto-lube you will need to up jet by around 5% on the main jet or it will run lean.
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Ducati 996 Biposto
Suzuki Goose 350
DT125R Supermoto (Project)

[ms51ves3]

[Rafe Dent]

Thanks for replies, great.

It is in fact a Mikuni 26, not 28, as I'm sure you all guessed. Sorry. And now I've got it all in bits and pieces on the kitchen table, it's all pretty much clean anyway, as I'm sure you all guessed as well. Got some sort of Wynn's acidic cleaner to make sure though, and left it all soaking. Unless the dog's got it.

But had a bit of a Eureka moment. The choke cable has been snipped off 6 inches away from carb - and I didn't quite dare admit it, but I trimmed it down even further and slid on a sort of screw grip to yank on the choke wire, whilst I wait for the new one to arrive at the shop. But when I tried this with the carb in pieces, I can see all the gubbins working all right, and looking through the barrel I can see broad daylight down the small choke hole, where the air must be rushing in (when choke's off).

Is this my problem, and should it all be airtight? Even when the new cable arrives it doesn't look like it'll be a 100% airtight fit around the cable ends.

The guy in the shop offered me a sort of stubby tap replacement, unfortunatley the screw fitting was too small to fit the carb body, but that looked like it would have been airtight all right.

Thanks in advance, Rafe
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Kawasaki 125 KMX - woods & tracks only

[Rafe Dent]

Turned out to be a missing washer !! Nothing to do with Eureka moment number 1 or 2, which I'm sure you all guessed anyway.

Between the main jet and the needle jet, I now know there should be a small brass washer. This had been left out by the guy who sold it to me, maybe after his rebuild/ clean - so effectivly the needle jet, along with main jet, had free play of about 1cm ! (Main jet same diameter as needle jet, so only held in place by locating pin lower down in needle jet housing). This caused extremely variable running conditions/ stalling, as I'm sure you can appreciate. Found small (steel, does that matter?) but right diameter washer hanging around workshop, to fix and locate needle jet on carb seating point, to hold the 2 jets as intended.

Only had a few minutes this morning to blast about, but all seems a thousand times better. Still waiting for choke cable to arrive, but I think the real problems are pretty much solved.

Hope this helps other carb newbies. And at least I know how carbs work now. Well, more so.
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Kawasaki 125 KMX - woods & tracks only

[ben350]

Not that washer that I mentioned in my post above then

PS upjet advice was erring on the side of caution
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Ducati 996 Biposto
Suzuki Goose 350
DT125R Supermoto (Project)