29th Apr 2007, 10:36

My KH125-K9 1996 has five gears, but anything over 3rd gear and I get no power.

I can get up to 50mph in 3rd, but in changing to 4th I end up dropping to 45MPH, I can't get anywhere near 5th gear.

I have used fully synthetic 2T oil, installed a new spark plug, installed new exhaust gasket and de-coked the exhaust, but still top out at around 50MPH.

What sort of speeds do you guys get? And what could be the problem with mine?

10th May 2007, 12:31

Kroninberg’s KH125-K


I can only get it to 50MPH in 5th Gear @ 5000RPM, will keep going, but I don’t want to bust the bike, on a typical day I will rev it up to 6500 ish.

--how high have you got to Rev your bike to get to 50MPH??

I’m using fully synthetic as well, but told I’m wasting my money, but sure it works so I am not changing.

Sorry lost as to what the problem is, but if I was guessing I might guess that your gears are in the wrong places, you're getting the same speed out of your 3rd as I get out of my 5th, maybe not wrong place, but sounds like the wrong gear selection, don’t know enough about bikes to know if this is even possible, but that is what it sounds like to me.


16th May 2007, 18:40

It is possible to have gear over selection problems. This occurs when you intend to change from 2nd to 3rd, but end up in 4th or 5th. This is the result of a defective detent arm that is external to the gear box. The detent arm is spring loaded, and seats against the cam plate on the selector drum to give precised gear selection.

A KH125 should easily do 55mph. The European model (not UK) that is 14bhp should probably do about 70mph. One other problem with the KH125 are the oils seal on the intake side of the engine sometimes go. Look out for petrol in the gear oil and gearbox oil consumption. With two-stroke engines, a good seal in this area is essential to maintain optimum reliability and performance.

The later KH125 (1992 and onwards) went over to 12 volt. Also the KH125 was in production well into the late nineties, and some of the earlier models (late seventies) had six speed gear boxes.

28th May 2007, 14:51

Kroninberg's KH125K:

Well mine's broke again. When I start up and move, all is fine for about 200M, depending on how much revving I do, but then it gets splutters and cuts out. When I check the plug, it's wet with "oil" I think, very wet. If I dry it off under a flame, it will go again, but same will happen again.

I had the my bike mechanic lift the cylinder head off last week to inspect how my recent bore had gone. When I looked at the nuts on the head tonight, they didn't look very clean (hadn't moved), in fact there was a serious amount of dirt on top of the head?? I thought this would have been clean'ish, not sure if he bothered?

I have cleaned the air filter to eliminate that, probably needed to be done anyway.

Charged the battery as well.

Any ideas? Losing heart.

Starting to look for a new bike.

7th Jun 2007, 06:49

I'm in Australia and I have an older mid 70's KH125 with the 6 speed. This old bike will easily run to 60+ mph. In a slightly modified form it ran out to a genuine 85mph.

The solid locking of the kickstart reminds me a little of hydrolock. It's when the fuel is left on and the taps leak, filling the crankcase with fuel. You kick the bike and it locks solid as the fluid will not compress. Could be worth checking your needle and seat in the carburetor.

If this is worn or has a foreign object lodging it open, then this would allow hydrolock as well as making the bike sluggish by causing an excessively high fuel level in operation. I'd start looking towards carby settings and take a few plug readings ;-)


17th Jun 2007, 16:59

Hello, I have a k10 model 1998. Mine is fully standard with 5 gears.

I would like to know if it would be possible to put a 6 speed gearbox in it? It tops out at 82mph at the moment.

I am also interested to know what difference a micron exhaust system will make, and a big bore piston kit?


27th Jun 2007, 10:49

Adding a micron exhaust (assuming you can get them for the KH125) will give you more pronounced power, usually between 7000rpm and 10000rpm. But you also have to re-jet the carb with a different main jet. This removes the notorious flat spot at about 6000rpm.

A big bore kit will give you better low to mid-range torque, because the greater the bore diameter to carb diameter, the greater the intake velocity. Also a big bore will increase the compression ratio due to the greater swept volume.

Safely you can go up to 2mm oversize from standard (using the original standard cylinder barrel). This will increase the engine displacement to 133cc approximately. Using after market big bore kits (eg; 150cc, 175cc etc) will give you loads of low end grunt, due to the greater boost in compression and better volumetric efficiency at lower RPM.

But be warned, large big bore kits result in huge pressure on the bottom end bearings and crank. Therefore the engine will last much less than intended. Only do this if you know

what you are doing. The 2mm oversize and the micron, as well as other minor mods should be fine and give miles of fun.

19th Aug 2007, 07:31


I have a KH125. I think it was registered in 1995. It goes great, but it won't tick over as the carb needle is broken. Any suggestions on what I can do, or will I have to invest in a new carb?

5th Sep 2007, 17:56

If the carb needle is broken, the needle being the one attached to the throttle slide, you don't need a new carb. All you need to do is order a new needle and needle jet from Kawasaki. It will cost about twenty quid, give or take a few.

29th Jul 2008, 12:08

Hi, I just bought 1992 KH125 and the kickstart shaft as snapped. I've ordered another, but not too sure how to fit it? Could anybody out there have any idea, and explain the procedure.

Plus the battery is flat; would I still be able to bump the bike with it like that, or do I need to buy new?


1st Sep 2008, 09:12

Does any one know where I can order a Kawasaki KH125 kick start shaft?

26th Sep 2008, 05:20

Kick start shaft for KH125; you will need a fly wheel puller, you can find them on ebay for about 10 quid. The fly wheel needs to be removed to replace the kick start shaft, which means splitting the engine open - not a job for yourself unless you know what you're doing.

18th Oct 2008, 10:55

Hi guys, I have a KH125-k5, and I'm trying to fit a new diode, but do not know where on the wiring loom it fits. Can anyone help?

25th Oct 2008, 17:45

Hey, I have a KH 100, and am having a few problems.

1. 5th gear in high revs/>55mph feels like it slips to neutral and revs fly up so I have to down shift.

2. Indicators either stay on solid or off completely when they are on and the brakes are applied.

If you have any idea what could be wrong with it please email at: cosstick@hotmail.co.uk

Many thanks, Simon.