[vern]

I have a 350 mercruiser. At cruise, the boat will cut out and die. The tank has been emptied and refilled. Once while cruising and the boat begain to cut out, I began to do S turns and the boat sputtered but continued to run.
Could there be something in the tank that floats or is pulled to the gas inlet causing the boat to stall? How does the fuel pickup work? Is it attatched to the bottom of the tank? Could it have broken loose?
The tank is half full...

[Hudson River Steve]

Could be something in the tank but more likely a cracked pickup tube or a split hose letting air into the fuel system.

[vern]

With a full tank, my 350 Carb mercruiser runs great. When it gets to 1/2 tank it will cut out in cruise. It then will start right up.
I have emptied all the old gas and replaced with new. All hoses look good,,Tank pickup is clean.
Any ideas,,,a friend said to replace the fuel pump,

[Hudson River Steve]

Did you check tank pickup tube for cracks?

[vern]

When I drained the tank, i checked the hose for cracks..would the boat stop and start if there was a crack? could there be sludge in the bottom of the tank that collects at the pickup site, then dispereses when the boat stalls out?

Could it be a bad fuel pump?

[Brian Belcher]

The full tank vs half tank cancels sludge/debris blocking it. It screams to me a bad pick up hose or a loose hose clamp.
Can you get to the pick up point of the tank ?
Do you have an in tank pump ? I'm looking at possible hose collapse due to suction and a weak walled hose

[vern]

I have checked and cleaned pick up point.
all connections are tight,
What do you think about the anti siphon valve or weak fuel pump

[Brian Belcher]

The anti siphon is only a pain in start up, especially after its sat a while.
I'm wondering about a very soft hose collapsing from suction. Weak pump would remain weak while turning, right ?
But, than again, why would turning cause a collapsed hose to, uncollapse?

Where is the fuel pump in your system ?

I edited cause I was very vague about the drain back valve.
The only purpose for this valve is to prevent fuel in the lines from draining back into the tank after the pump is turned off. That's why I said I doubt it's the valve. Your problem is after it starts.

Does your boat start cutting out immediately after starting ? Or does it need to be at full operating temps? In 40+ yrs of working on engines, I've never seen an actual vapor lock and I know that's not your problem.
Temperature could affect the gas tank by expansion. It's just one of the possible problems.
I really need to know if yours is pressured by an electric pump (in tank) or is it a manual pump on the engine (most likely).

[vern]

Hello

The pump is located on the engine..it is an old mechanical pump.

i do not understand...running fine, then stops. Starts right up, and cruises normal..
this only happens with a fuel level 1/2 or below.

[Brian Belcher]

Vern. You are obviously loosing the prime and it has to be in the line in the tank. Full tank to half and the bad spot is covered with gas. Once you use enough gas to expose the bad spot, not covered anymore, the prime is lost. You are going to have to pull the pick up unit completely out of the tank. Block off the lowest opening on unit, where the gas is actually drawn in at and put a small vacuum to it. You can use a brake bleeder pump, or a fish tank aerator pump.
The fact that gas level has everything to do with it is the smoking gun. I've looked everywhere for a pic of the pickup unit to no avail. Do you have one ?
What is your gas level right now ?