I'm sure that fan isn't setup to run on A/C Power either. You would need to get a Rectifier to convert to DC.
But like dakota mentioned, 4Amps at 12VDC will be pretty much maxing out the blaster's electrical system.
If you wanted to run the fan automatically off a temperature source, you can use a thermocouple around the spark plug then tighten it down in the head, that is how TrailTech systems get their temp readings for air-cooled engines