FAA Powerplant Written Practice Test

What is likely to happen if a spark plug is gapped too wide?

1. Engine overheating

2. Hard starting

3. Increased fuel consumption

4. Reduced oil pressure

The correct answer is: Hard starting

When a spark plug is gapped too wide, it creates a larger distance that the spark must jump to ignite the air-fuel mixture in the cylinder. This can lead to hard starting for several reasons. First, the wider gap requires a higher voltage to create a spark strong enough for ignition, which may not be achievable under lower battery or starter conditions. Second, if the spark is weak due to inadequate voltage, it may not ignite the fuel mixture efficiently, resulting in misfires or incomplete combustion. This can make the engine difficult to start, especially in colder conditions or if the fuel mixture is not optimal. Hard starting becomes a pronounced issue because the spark plug’s performance is critical during the initial engine cranking phase. If the electrical system cannot provide sufficient voltage to bridge the wider gap, the engine may not start at all, or will require multiple attempts to turn over.