Hi Danny,
Yes they a crap idea but we are stuck with the design. If you look at the primer bulb it has a hole in it. When you press your finger on it, it traps air inside the primer cap and this increase in pressure is designed to push a squirt/dribble of fuel into the inlet manifold. The problem with this primitive design is the reason people have different ideas on how many times to pump the bulb, because they vary so much.. It is something you have to work out what works best on your mower. As I said an absolute crap of a carby design but it is what we have to work with
