Upgrading the Jetting on a Kawasaki KLX 140
By Marcus Wilcox

Revised: 2/21/2013

I have two 2009 Kawasaki KLX 140 motorcycles for the kids.  They are jetted extremely lean, making them hard to start and slow to warm up.  In addition, the fuel screw is not adjustable from the factory.  There are some posts on the web discussing what upgrades work, but no installation guides.  Below are instructions to upgrade the pilot jet, main jet, fuel screw, and add a fuel filter.


To Purchase



Removal of Carburetor

Replacement of Jets

Modification of Fuel Screw

Installation of Fuel Filter

Shimming Slide Needle


Set Fuel Screw & Idle Speed

My Experience
The bike used to require full choke, extended turning over, and possibly a squirt of starting fluid to get it started.  I retrofit two KLX 140s with the modifications above and they both started without choking within 1 or 2 seconds of cranking over.  A ride on each showed them to be substantially improved in power, responsiveness and time to warm up.
Cautions & Recommendations