1983 Mercruiser 470 Runs fine then loses RPMs slowly then dies

[bucklahoo]

1983 Mercruiser 470 Carbureted 4 Cylinder. Wellcraft V20 Steplift.
Started fine, idle good and smooth, temperature normal. Around 1000 RPMs from dock to main lake for about 10 minutes ran ran and sounded smooth. Took about 15 minutes cruising at 2500-2750 RPMs then all of a sudden the RPMs slowed to 2000 for a few minutes then eventually slowly died. Let it sit and fished for a while, started back up then did the exact same thing on the way back dying after the 15 minute return journey. Temperature constant throughout. Also had a moment where RPMs dropped, I kept the throttle where it was and after a few minutes RPMs increased back to that original spot. New fuel pump.
Maybe time for a carb rebuild? Any other thought? Thanks

 

[Bondo]

Ayuh,..... Welcome Aboard,...... Do ya have a canister type fuel filter,..??
If not ya should add one,....
If ya do, dump it into a clear container, 'n look for anything but clean fresh gasoline,.....
It could also be the tank, the dip-tube in the tank, or the anti-siphon valve at the tank's outlet,.....
Diagnose it before ya start throwin' parts at it,.....

 

[achris]

Could also be a blocked tank vent line. Next time it does it, unscrew the fuel filter cap. Listen closely as you do, you may hear air rush in. If you do, that's a blocked tank vent.

Chris...

 

[kenny nunez]

After checking out the fuel system try this.
The only other thing that I have seen do what you are describing is the resistor wire. Just secure a volt meter on the + side of the coil next time out and check if the voltage drops below what it was when you first started the engine. If you have a spare rotor try installing it when the engine stops, sometime depending on the quality of them they will go to ground when they get hot. The genuine Mercruiser rotors have a slightly longer blade which tightens the gap to the contacts in the distributor cap.