Bubbles in the fuel line means either a suction air leak, or a blocked fuel tank air vent. If it was the fuel tank air vent it would not run properly after starting, so a fuel line air leak is more likely - but check the tank vent anyway, because a high enough vacuum in the tank can cause the fuel pump to misbehave.
Check for air bubbles in the primer bulb when the engine is running - air may be entering the system steadily, but once the fuel pump starts operating, it has enough capacity to pump air and fuel simultaneously.
You would not necessarily get a fuel leak if there is an air leak upstream of the fuel pump or primer pump. Liquids are much easier to seal than air - a pinhole air leak will stop the primer from working but may not leak fuel at all.
If you are sure that there is no air leak into the fuel pump (which is under suction when you operate the primer, remember) or a malfunctioning fuel pump valve, then check the joints in the various hoses attached to the fuel pump and the primer pump.
