The ignition coil sends voltage to the spark plug when the engine is running. A defective ignition coil may prevent the engine from starting. As with the spark plug you can use an ignition tester to test the coil to determine if the components have failed.
The primer bulb draws fuel through the carburetor when pushed to prime the engine when first starting. Over time, the rubber can become brittle and crack, causing the bulb to leak gas. Installing a new primer bulb will fix the problem.
Over time, the carburetor itself may develop cracks due to vibration and the heat of the engine and begin to leak gas. You should inspect the carburetor for cracks or corrosion and replace it with the new one if necessary.
Various float assembly components inside the carburetor bowl can be defective as well. The float needle opens and closes the float valve to allow fuel to enter the bowl. If the float needle or the float itself is damaged, the carburetor may continue to fill with fuel until it overflows. You should be able to stop the leaking by replacing one or more of these components.