The Powermax cans are primarily for filling on-board tanks with liquid gas. Most modern Auto-start engines now have a pulsed metering facility for introducing gas in a controlled way that allows only gas to enter the engine, and hence no flames (normally) out the back.

As said previously, if you are connecting the Powermax directly to the engine it has to be inverted.

If you are using the Trigger Valve, (Usher Enterprises) then pushing the trigger forward instead of squeezing it, allows constant gasflow without having to handle the can at all during the start-up.