If the engine won’t crank, the battery may be low on charge or expired. It will need to be fully recharged (or replaced) on the ground before flying. Most aircraft batteries have a lifespan of about 5 years. Flight should never be attempted with a battery that isn’t fully charged since you will have no electrical power if the alternator fails.

If the engine cranks but doesn't start after a few revolutions, it either doesn't have enough fuel or it has too much—either prime it or clear it but don't just keep cranking or you'll overheat the starter. If you suspect the engine is flooded (smell of fuel in the air), follow the checklist procedures in the POH.

Sometimes during cold weather the fuel will not vaporize properly because the vapor pressure is too low. Follow the cold weather starting procedures in the POH.

If the vapor pressure is too high (from hot weather or engine heat), the fuel can "boil" in the lines of the fuel system. Fuel vapors released in the lines by this boiling have a tendency to collect in high points and cause a vapor lock. A bubble of fuel vapor in the line can prevent the flow of fuel from the tank to the carburetor or fuel pump. Fuel injected engines are known for being difficult to start when the engine is hot because fuel vapor prevents the liquid fuel from reaching the nozzles. Before an effective start can be made the lines must be purged of all vapors. If there is no specific procedure described in the POH for your aircraft, the following method can be used: 1. Place the mixture control in the Idle Cut-Off position and open up the throttle so the boost pump can operate at full pressure. 2. Turn on the boost pump and allow fuel to circulate through the pump for 15-20 seconds. 3. Turn the boost pump off and place the mixture control in the Full Rich position. 4. Close the throttle to the correct position for starting and engage the starter. The lines up to the fuel pump and the pump itself should now be full of liquid fuel and the engine should start normally.