1988 4.3L merc. stalling

[Sdraves102]

I have a 1988 4.3L mercruiser inboard that starts well, runs at top speed well for about 5 minutes than slowly losses power.
If you slow it down it will stall out completely and you can't restart it. If you can restart it you have to give it full gas to get it to chug to shore at 5 MPH. You have to keep restarting until the battery finally dies. This has a 2 year old new Distributor, new cap and new sensor or sender. It has the old Thunderbolt IV. New every thing except fuel pump, coil, IV box and carb. Any ideas I'm at a loss what to do next. The engine doesn't even have time to get warm before it acts up.

 

[Bondo]

Ayuh,...... Welcome Aboard,...... It sounds like it's starving for fuel,......

 

[alldodge]

Agree with Bondo, no fuel

New every thing except fuel pump

Pump is probably barely working so if you get it to started when cold the pump works a bit better. Tt gets weaker till it can't supply much of any fuel.

Remove the fuel line at the carb and place a Tee fitting with a fuel pressure gauge. Pressure should be 3 to 7 psi

https://www.amazon.com/ABN-Vacuum-Fu.../dp/B079P3DQPQ

Or attach gauge straight to the fuel line a put just a slight bit of gas down the throat of the carb to make it run to see pressure

 

[Rick Stephens]

There are a number of places in the fuel system that can be plugged up. So start as advised by checking if you have fuel pressure to the carburetor and start backwards. Not enough pressure is not necessarily a bad pump if the fuel line is bad or the anti-syphon valve at the tank is plugged up.

 

[Sdraves102]

Thanks for the advice good place to start. Could you fill me in on the anti syphon value a bit more don't want to miss anything.

 

[alldodge]

The antisiphon valve is attached to the fuel tank and the rubber fuel line attaches to it. It is a spring and ball to keep gas from siphoning into the bilge if the line breaks.

 

[Bondo]

Ayuh,..... Cool graphic AD,.....