Yamaha 250 issue

[abl1111]

Troubleshooting the system based on some of your input. The fuel filler and the vent line are both in the very back of the 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.

We checked the Perko breather caps ability to breathe when closed - it does.

Is there anything else we're missing ?

If we could confirm it's one thing or another, then we'd focus there - but for now, we're at;

- something randomly clogging the pickups at different times even though the fuel tank has been polished twice
- a vacuum issue due to venting problem

If I knew it were a venting issue, an option could be to empty tank and have a new vent hole drilled into the tank more forward.

Any new ideas based on the above ?