In this month’s tech talk, we will go over how to replace the throttle return spring on a Mikuni TM40 carburetor that’s often used as an aftermarket option on the Suzuki DR650, Honda XL650L, and Kawasaki KLR 650. Many of our customers feel that the stock spring is too stiff, making it harder to rev up their bikes and straining their wrists on long rides.
Once you’ve removed the carburetor from your bike, the first step is take out the roll pin that holds on the pulley on. You can use a 7/64” drift punch or drill bit to push the roll pin from the cylinder side of the carb. You can use a pair of pliers to gently help the process along from the other side.
Once the roll pin is out, you can remove the throttle cam, plate, and spring. Spin the cam to remove tension from the spring. You can then remove the two screws securing the plate, and remove the plate.
To reassemble with the lighter spring, first hook the spring onto the keeper. Then secure the plate using the two screws. Hook the spring to one of the three pegs on the cam (depending on how much tension you want), and give the cam a full clockwise turn to add tension. Lastly, reinstall the roll pin once you have everything lined up.
As always if you have any questions, please don’t hesitate to contact us!