How do you fix a leaking carburetor on a Yamaha Blaster?

First it depends on where it is leaking and what is leaking. IF it is leaking fuel out the drain hose, then remove the shut off screw from the bottom of the float bowl. You can clean this out using carb cleaner with the straw. Carefully inspect and clean the shut off screw. I have polished these with ultra fine emery cloth. this should stop the overflow leaks. Also, you might want to pull the float bowl off and make sure the float is not stuck allowing fuel to continullay flow into the bowl. IF it is allow air to leak in, then check the carb top gasket and the intake boot for damage.