Another way of doing it without shutting the engine off was to run a manual choke. You pull the choke on to richen the mixture wait a couple seconds then push the button to light em off, would continue to burn as long as there was unburned gas in the exhaust. (might be why so many cars had melted taillights)

 

Used to have a 81 F-150 with the 4.9 that ran real rich thru the single barrel carb...I could get around 45-50mph...drop into second, gun it and then pop my foot off the gas to get a nice detonation. Yeah it was most likely tearing up stuff in the engine but the flame that shot out the tail pipe and the rip in my muffler was great at night. That old truck didn't get up and go for nobody so I always had people tailgating me trying to get on the freeway and such...at night...pop the pedal as above and people strangely enough got off my bumper.