Pressing the gas pedal and pulling on the throttle lever do the same thing, including actuating the cold start system. If the throttle lever is up (or the accel pedal depressed) while the engine is cranking, the cold start valve is actuated.

That said, although this only seemed to happen once, it sounds like you have a gas leak leak. Was the fuel leak at the rear? That's where the fuel pump is, and my guess would be a leak on the pump output (high pressure) hose. But you really need to get under there and have a good close look. Keep a fire extinguisher close at hand.