kawasaki kmx 125

davidjg · L Plate Warrior Joined: 03 Jun 2006 Karma :

kawasaki kmx 125
how can i derestrict this engine can any one tell me how ?

kintheuk · Two Stroke Sniffer Joined: 29 Apr 2006 Karma :

If I remember rightly from when the kmx first came out it had (and I may be wrong) a piece of metal in the exhaust header and also as the euro versions had KIPS (kwak powervalve) which wasn't set up in the uk the valve needed rotating to the open position which increases the exhaust 'volume'. I could be wrong it has been a while since I have spent much time reading about 125s.
HTH

Keith

Finglonga · World Chat Champion Joined: 27 Jul 2004 Karma :

davidjg · L Plate Warrior Joined: 03 Jun 2006 Karma :

thanks for that but how is it done :?any idea of a web site that covers it and tells you step by step Idea

kintheuk · Two Stroke Sniffer Joined: 29 Apr 2006 Karma :

If it is restricted as I thought then first off you need to remove the exhaust.
IIRC you will see the washer (?) inside the exhaust header (nearest the cylinder head) and it will be mounted to the outer edge of the exhaust at at least two points. With a flat file or maybe a hacksaw blade you should be able to remove the section of weld that holds it in place and remove the disk

If you have the blanked off KIPS valve then you just need to remove the cover and rotate the valve. It will be logically positioned at the front of the engine on the exhaust outlet.

I am fairly sure the de-restricted KMX was good for 21bhp, you are doing all of this at your own risk as the extra power will put more strain on the engine and almost certainly will reduce its life expectancy. If you are not happy to do this and worry about your own mechanical experience then don't do it.
After removing the washer and altering the valve you may need to re-jet the carb. Also there is a chance that there is a piece of rubber inserted in the space between the carb and airfilter.

I found this in the VD archive:
jjones12-Sep-2003, 19:35
newish ones there is a restricting rubber sat between the carb and airfilter. just remove it.

remove the exhaust there *may* be a washer welded in it where it leaves the head. remove it if there is.

Check this also
https://www.landrovernet.com/forum/showpost.php?p=284610&postcount=19

stevo as b4 · World Chat Champion Joined: 17 Jul 2003 Karma :

Later KMX's certainely from 97 onwards have only one restriction. It is a welded in restrictor in the entrance to the expansion chamber, it looks near enough the same as the NSR125 restrictor with 3spot welds, that more people on here are aware of.
No rejetting is required on any u.k spec and most european spec bikes. It will then have 24bhp or between 20-21bhp at the rear wheel. This is enough power to redline the kmx125 in 6th, and gives 80mph on std 14/48 final drive gearing. However you can fit a 15t front sprocket to up the top speed to about 85mph, which is better for road use, and still allows good acceleration. If you tune the engine closer to 25bhp at the wheel then it can pull 16/50t gearing to give almost 90mph, but with less acceleration. 15/48t is the best gearing compromise however!

There's no restrictors in the carb-airbox duct, or carb-reedvalve manifold. The KMX125 does have a restrictive airbox lid however that is not a restriction as such, but it hampers airflow and by modifying the lid and re-jetting gains of 1-2bhp have been seen on KMX's that have been dyno'd before and after.

There's plenty that can be done to tune the KMX like any other 125 really, but when in full power form it's as quick as any of it's rivals and as fast as you would want from a trailbike 125.