Carb on fire???

[macc nova]

Yesterday when i went to start my car after work and the carb was struggling to get enough fuel to the engine, this happens quite regularly so i know how to fix it. (just bought a weber thats replacing it) but anyway i took it off then made sure was no blockages and then put it back on. When i tried to start the car again he carb set on fire and i have no idea how this happened?? anybody got any ideas as its never happened before???

[Adam]

Yeah fuel ignited up the inlet.
Lean mixture can sometimes cause it, as can incorrect ignition timing(too retarded)