A multiple fuel tank purge system and method includes providing a pair of fuel tanks, including a main fuel tank for containing impure fuel and a separate, auxiliary fuel tank that contains commercial canned fuel. The engine runs on the impure fuel from the main fuel tank while the engine is in normal use, and then employs a shutdown cycle that switches to the commercial canned fuel from the auxiliary fuel tank for some pre-set time period. This arrangement allows the engine to be purged of the impure fuel (by burning the impure fuel during the shutdown cycle) and replaced by the commercial pre-mixed fuel before the engine is finally shut down. The system may further include a novel fuel cap with a fuel line, a tank within a tank fuel container, and/or an electronically actuated shutdown cycle mechanism.