Did you just replace the burned-out ignition coil so that the new one also burned out? That's why!
The main cause of premature ignition coil failure is a worn or damaged spark plug ignition cable.
A damaged spark plug ignition cable will have a much higher resistance than normal. This high resistance can cause the secondary winding of the ignition coil to develop a very high voltage. This excessive voltage generates a lot of heat, which melts the wire insulation of the coil.
Remember, Voltage = Amps x Resistance
In the example below, the resistance of the damaged spark plug ignition cable reads 5 megohms. That's 5,000,000 Ohms! We know that a typical small engine ignition coil uses 3 to 5 amps. Through the above mathematical formula, we can determine that the spark plug ignition wire is broken, causing the ignition coil to generate 15 million to 20 million volts!
Remember that when you are working on an engine, it is best to determine the cause of certain failures before purchasing parts to avoid costly repeat failures.