07/24/2020
Just passing this on. It's helped us in the past. We are not Marine Outboard Mechanics. This is just a guide we've used.
PRIMER BULB AS A DIAGNOSTIC TOOL
The primer bulb is also a diagnostic tool that will tell you a number of things about your fuel system.
STALLING OR RUNNING ROUGH AT SPEED
If your engine begins to stall or run roughly several minutes after starting and when running at higher speeds, use the primer bulb to force fuel to the engine. If this restores the engine to smooth running, you have a fuel supply problem. There may be a restriction in the fuel line, or your engine fuel pump could be defective. If this happens even at idle speeds, the primer bulb may not be working properly.
PRIMER HARD TO PRIME
If the fuel line is difficult to prime, you likely have an air leak in the system. Check all fuel hose connections. You could also have a defective primer bulb, or not be orientating the primer bulb properly during priming. A likely place to investigate is the fuel disconnect on the engine. Be sure the connector is properly seated and is making an air-tight connection.
COLLAPSED PRIMER BULB
If the primer bulb collapses after the engine has been running or stays collapsed while priming this indicates a fuel line restriction upstream from the primer bulb. A defective check valve in the primer bulb could also be the cause. The fuel line filter or the fuel tank pick up could be blocked. A blocked fuel tank vent could also cause this. A quick way to check the tank venting is to temporarily open the fuel tank filler fitting. For some reason the fuel tank vent line thru-hull fitting is a favorite spot for wasps to build mud nests.
BULB NEVER GETS FIRM
If you can fill the bulb with fuel but it never gets firm, you probably have a fuel leak downstream of the primer bulb. This could be a stuck float valve on a carburetor, or a fuel leak in the engine fuel pump. Many engines use a diaphragm pump, and if the rubber diaphragm has a pin hole leak,
