I’m new to four-strokes. Can you tell me what an accelerator pump does?
An accelerator pump is nothing more than a plunger that is designed to temporarily richen the mixture until the engine can produce enough air flow to pull the fuel through the jets. Just like a bathroom plunger, a rod pushes on a rubber diaphragm,which plunges into a reservoir of fuel, forcing the fuel into a small orifice, which leads to the intake tract. When you turn the throttle, a cam is activated by an adjuster screw to engage an arm that pushes on the rod. It sounds complicated, but just think of a toilet plunger.