Flames after starting
It isn’t unusual to see flames from the EC 120 exhaust after a less than perfect start. Indeed if there has been a botched start or two you can just about put money on seeing flames. The reason for the flames is the start injector ventilation process that follows a start.
Following each start (or attempted start) the start injectors are ventilated with P3 air from within the combustion chamber casing as soon as one releases the start switch. This ventilation air drives all the fuel remaining in the start injectors and their supply lines down into a small collector tank mounted under the rear part of the engine. The tank is about 3 inches long and around 2 inches in diameter. A vent pipe from the rear of the collection tank goes upwards and terminates in a rearward facing outlet inside the bottom of the exhaust tail pipe.
After a normal start the small amount of fuel drained into the collection tank evaporates and is drawn into the exhaust stream. However, if there is an aborted start or two the collector tank can end up nearly full of drained start injector fuel. If this is the case there can be a spectacular fire with blobs of flaming fuel showering the front of the tail boom when the engine finally starts.