1999 Johnson 115 Losing Fuel Prime

[Captain Jeff]

Hi, My 1999 Johnson 115 (60deg V4) loses fuel prime when not in use and is difficult to re-prime. If the boat is not used for a day, or possibly even hours, you will need to pump the primer bulb and it is difficult to get a good prime. I can hear air bubbles going through the bulb while pumping and the bulb never truly gets firm, only slightly firmer than it was. I can also see some air bubbles in the clear plastic fuel/oil connector where the fuel line connects to the engine.

When running, sometimes it will run great, other times it won't. Last night it would run okay under around 2,000 RPM and sometimes bog and want to stall. Pulling it back to idle would keep it from stalling. If I was able to get it on plane, it would run okay at higher RPM.

I have replaced the 3/8" fuel line from the tank to the water separating fuel filter all the way to the engine. I also have tried two brand new primer bulbs. No fuel leaks out inside the engine compartment when I pump the primer and I can usually hear the air releasing from what I imagine is the vapor separator. I am pretty confident there are no leaks in the fuel line to the engine. It seems like something is going on in the engine (i.e. air leaking back into fuel supply) that is causing it to lose prime. Your help is appreciated.

 

[Chris1956]

The gasoline line should not have any bubbles. If you hear bubbles in the primer, look upstream of the bulb, for air leaks at every fitting.

Priming the motor every day is normal. You should not need to prime it if you sit an hour or so.

 

[BillP]

Fuel pump diaphragm may be getting porous and not able to maintain full suction. The o-rings in the fuel line connectors don't last forever either...I pull the old rings out and replace as normal maintenance.

Are you pumping the fuel line when it want to bog down at speed?

 

[Captain Jeff]

Thanks for your help guys. I will check it out tonight.

BillP, what o-rings are you refering to? Those on the plastic connectors to the VRO? I have the VRO by the way, not the normal fuel pump. Thanks

I will pump the primer bulb when it is bogging and it will run better.

 

[Chris1956]

Check gasket and Oring on main strainer under the airbox. If that leaks air in, it will cause issues, like extra oil being mixed into the fuel.