low water flow shut off?

[dirtdad]

Maybe a stupid question. On a 4.3 carburated motor, is there something that shuts off the motor if there is low water flow? Running in my driveway using earmuffs and a garden hose, it runs fine for a couple of minutes, and then shuts off. New distributor cap, rotor, plugs, electric fuel pump, cleaned and rebuilt carb, emptied fuel tank of all old gasoline, cleaned fuel pick up tube (it was clean, as well as the screen at the bottom of it), cleaned antisiphon valve, and every time I have tested the oil pressure/fuel shut off switch, it tests fine. So. I'm wondering if there is something that is shutting off the motor, there are no alarms going off, nor do I know if there would be.
Thanks.

 

[QBhoy]

Not that I'm aware of. It would just keep running...at best with an alarm in the form of beeping.
Someone may correct me, but I'm pretty sure I'm right.
Is it maybe just the choke coming off and perhaps the idle speed is needing adjusted ?

 

[dirtdad]

very frustrating. I have owned this boat since new, 2001, and have never had any issues. never had the carb apart, the plugs I changed were like new. 419 hours on the boat. The fuel pump did go bad, I ran power diectly to it, and it just clicked, the new one turns, but everything else seemed fine.

 

[QBhoy]

Have you checked the auto choke function? Most guys over here disconnect them after a few years.

 

[muc]

You are describing a classic failure of the oil pressure switch that controls the fuel pump once the motor is running. Might want to check it.

Edit. Is see you have checked the switch. Have you checked for power thru the switch to the pump?
Note: MerCruiser recommends that the oil pressure switch and the fuse that supplies it be changed anytime the fuel pump is replaced.