Join Date: Sep 2005
Thanked 228 Times in 170 Posts
ATV: 2013 550 XT
Fuel flows from the tank to the carb. The float governs when and how much fuel is delivered to the bowl. As fuel collects in the bowl, the float raises and pushes the float needle into the needle seat, therefore cutting off the fuel supply to the carb. That's why if you have crud wedged in the needle/seat area or have a sticking float that you'll have fuel drip from the overflow tube as it's causing excess fuel to run into the bowl.
So, now you have fuel in your bowl. The jets allow fuel to get sucked up from the bowl and get mixed with the incoming air and get delivered to the cylinder. You have a needle connected to a slide (also called a diaphragm on your carb). This needle goes down into the main jet. It "plugs" the main jet when the slide is all the way down. As you give it throttle, the slide rises up, and the needle too rises, and unplugs the main jet. This is where the taper of the needle comes into play. The higher the slide moves, the less the needle is restricting fuel from the main jet.
Does that help?