captain swag said:
Had a similar problem. I would come back to the boat after it sat dormant, maybe an hour or two and the primer balls were flat. It sounds like you are losing prime. Check connections for an air leak. Maybe a leak around a seal on the separator/fuel filter(s), hose clamps or brass threads at the tank pick up. Temporary installation of some clear fuel line will show air bubbles and might reveal something. Also make sure to have the primer bulb as level as possible at rest or better yet elevated discharge side up. this allows air to be more readily purged. Confirm that the primer ball is installed correctly, ie check the direction of fuel flow to the arrow on the ball. Hope this helps.
If you have an air leak, either before of after the primer, the bulb will not go flat. It may get soft but not flat. It only goes flat when there is an upstream (bewteen bulb and tank) restriction to flow. Running with the fill cap open is a way to see if the vent is blocked. If the bulb doesn't colapse, then the vent is bad.
Even if you don't have a screen on the pickup, it can be blocked by something in the tank. A common culprit is the round flat seal from the cap of an additive. Others have dropped bottle caps into the fill. I have experienced leaves plugging the pickup.
There is also a posibility that the fuel hoses are colapsing or restricted on the inside. This seems to be common problem on older mercury riggings but is not related to Mercury per se but the hose they used at the time. It can quite frustrating to identify a colapsing inside wall of a fuel hose since often the outside often looks normal.
I am sure you checked that the primer is installed in th correct direction
Good luck
