Port engine cuts off after about 15 minutes

[Ctmangrum]

I have a 1976 mariner with a Ford 351 Windsor. After idling or running in gear for about 15 minutes it will cut off. Engine doesn't show that it's overheating and battery indicator shows it has power so I'm not sure what's going on I'm able to start it back up as long as I have juice in the battery Change the coil, thinking that was the problem but didn't resolve it. Coil has an internal ballast resistor as recommended prior to the ones I installed, it did not have a resistor. Could use some advice. Thank you.

[km1125]

How quickly does it restart after it stalls? Do you need to do anything to the throttle to "coax" it to restart, or just hit the key? How well does it idle before it dies?

[buster53]

With the possibility you have a partially blocked fuel tank vent, simple solution, take the fuel tank cap off and see what happens.

[bud37]

Is this a continuation of your original problem, is the other engine fine now ?? Before both engines were acting up and you were going to upgrade the ignition. Have you changed ignition systems to both engines ?

Is it only when running in gear or does it also happen when running in neutral ?

[Ctmangrum]

So the other engine is fine now. Never upgraded to electronic. Bought a couple aftermarket distributors that the were just shy of clearance for the cap and decided to just go back to points for the time being. Stbd stalls whether its in gear or at idle but takes about 10-15 mins. Never messed with this engine except for looking around to compare to the port side. Someone had suggested checking fuel
Vents, lines, etc. Try running it with the fuel cap off to see if venting was the problem. Haven't looked at the fuel pump yet to see if its failing. Not sure where to hook up the pressure tester since iv'e never done it before. It wouldn't go where the sight glass would be would it since if their was fuel in there I would know the pump was failing and I wouldn't have to test it.

[Ctmangrum]

Update: Took the gas cap off to see if I had a clogged fuel line vent but still didn't keep it from stalling. Nothing obvious on the carburetor or anything else that I can think of so time to call in a professional.

[bud37]

Earlier you said something about gas in a sight glass ?....where is this glass ( top of fuel pump if mechanical or before carb like a prefilter) and is it glass or plastic ?

[Ctmangrum]

I dont remember mentioning that, may have been someone elses reply. No gas n the glass

[bud37]

Source of the post Not sure where to hook up the pressure tester since iv'e never done it before. It wouldn't go where the sight glass would be would it since if their was fuel in there I would know the pump was failing and I wouldn't have to test it.

This is what I was referring to.

[Ctmangrum]

So I was never able to find a mechanic that would work on my boat and even the shipyards flaked. But, I do have a little more info. Port will run for about 15 minutes before it starts to sputter in idle and if I put it in gear while its sputtering, it dies. So its only an issue when Im coming into dock and im just "bumping" it to get into the slip and it stalls. At a loss.