Got a question for you guys - my brother is running (2) 2007 Yammi 250's with 300 hours and has been having the same issue for 2 years; either engine will suddenly die under way. The offending engine's priming ball will be totally sucked in. Not sure if it’s related but sometimes it happens after he refuels - can be either engine. Happens randomly.
Remedies tried
- New fuel lines from tank senders thru to engines including fuel priming balls
- All new fuel filters within each engine as well as water / fuel separator.
- Fuel tank polishing 2x ( after the first cleaning, an engine stalled and the guy came back did it again )
- Perko fuel filler with an integral breather vent in cap. This all seems to function - We checked the breather cap’s ability to breathe when closed - it does.
After 15 hours of use, it just happened again..
Engines are professionally maintained - the Yamaha guy thinks it's something in tank - he's at a loss...
Vapor Lock Theory
The fuel filler and the vent line are both located at the very back of the fuel tank which seems like a bad idea. I can see how with a 3/4 to full tank that the vent and fuel fill lines would be submerged under fuel while under way ( the gas would all be aft ). This could create a vapor lock as the fuel would be obstructing the ability of the vent to breathe. And, its possible that the engines fuel pump would suck the primer ball in, starving for fuel.
However, you would think that once the boat was stopped - the fuel level would normalize. And, when the fuel cap, which also houses the vent line breather were opened, the primer ball would fill back up - this is not the case. The primer ball stays sucked in. The only thing that remedy's this has been to wait and sometimes, infrequently if you turn off and re-start the other motor - the ball will normalize.
Fuel Starvation Theory
- something randomly clogging the pickups at different times even though the fuel tank has been polished twice
Water Fuel Separators filter size too small . Possibly switch the 10 micron water / fuel separator to a 20 micron one
Any ideas ?
Remedies tried
- New fuel lines from tank senders thru to engines including fuel priming balls
- All new fuel filters within each engine as well as water / fuel separator.
- Fuel tank polishing 2x ( after the first cleaning, an engine stalled and the guy came back did it again )
- Perko fuel filler with an integral breather vent in cap. This all seems to function - We checked the breather cap’s ability to breathe when closed - it does.
After 15 hours of use, it just happened again..
Engines are professionally maintained - the Yamaha guy thinks it's something in tank - he's at a loss...
Vapor Lock Theory
The fuel filler and the vent line are both located at the very back of the fuel tank which seems like a bad idea. I can see how with a 3/4 to full tank that the vent and fuel fill lines would be submerged under fuel while under way ( the gas would all be aft ). This could create a vapor lock as the fuel would be obstructing the ability of the vent to breathe. And, its possible that the engines fuel pump would suck the primer ball in, starving for fuel.
However, you would think that once the boat was stopped - the fuel level would normalize. And, when the fuel cap, which also houses the vent line breather were opened, the primer ball would fill back up - this is not the case. The primer ball stays sucked in. The only thing that remedy's this has been to wait and sometimes, infrequently if you turn off and re-start the other motor - the ball will normalize.
Fuel Starvation Theory
- something randomly clogging the pickups at different times even though the fuel tank has been polished twice
Water Fuel Separators filter size too small . Possibly switch the 10 micron water / fuel separator to a 20 micron one
Any ideas ?