Primers
The primer on the Cessna 152 routes to the front two cylinders only, presumably this is so that when the even worse pre-solo students flood the thing it will start too! One other thing, the copper primer pipes can become work hardened and shear at the connection to the cylinder - check it on the DI, as pilot may end up pumping fuel on to an engine and as it starts and heats up = fire! I speaketh from experience.