Have had a self-extinguishing tailpipe fire during a second start following IGN failure on a B737. After our first start attempt(s) with a failed igniter, we pulled back onto stand and got an engineer to inspect and ADD the failed igniter iaw the MEL.
Second pushback, engine start - all appeared absolutely normal in the flight deck. We received a cabin crew call (unusual - they wait until taxi before giving the cabin secure) - the no. 1 had had a call from the back that passengers had seen fire/flames in the engine, were concerned, and had contacted the rear crew, who informed the no. 1.
We asked the chap on the headset (Czech, but who spoke good English) if he had seen anything unusual during the start. "Yes there were flames but it's all OK now". Good job he was there to monitor the start, eh?! Anyway, fairly obvious that the 'fire' was just pooled fuel from the first failed start attempts and that nothing was wrong with the engine. Pax PA made along the lines of "you know what happens when you put too much lighter fluid on your BBQ..?" and all normal after that.