Primer bulb. The primer bulb draws fuel into the carburetor to make the engine easier to start.
Fuel filter. If the fuel filter is clogged, it will restrict the flow of fuel to the carburetor. As a result, the engine may not start.
Air filter. If the air filter is clogged or dirty, the engine may not start or may run rough.
Fuel tank vent (also called a check valve). The fuel tank vent allows air to re-enter the fuel tank. If the vent is clogged, the engine may stall.