3.0L/3.0LX Coolling Issues

[97_Manta_Ray_CR]

First off thank you for taking a look at my question/concern...

Over this last off season I replaced my thermostat, have had no issues to speak of, after taking the boat out a few times I noticed that the boat has a hard time trying to stay at idle (It runs rough) while in the water. At 4000 RPM boat run fine with no issues, I took a buddy out yesterday and explained some of my issues to him, He is a auto mechanic and he looked at my engine and felt the cooling hoses and said: (Yep there's your problem) he felt the two cooling hoses and the elbow hose (the one from the engine) was pretty hot and had soft, while the outlet hose from the thermostat housing was cool and hard. He said these two hoses should be the same temp and same pressure. So in turn whats he saying is that the electronic choke is calling for more fuel at idle and choking the engine out, because of the engine thinking the temp is off

The gauge on my dash never gets above 140 F

So my question is: is he correct and should I try to replace my thermostat again

 

[Bt Doctur]

Evidently not a marine mechanic,or familiar with electric chokes. Boats run a open system there should be no pressure felt on any of the hoses unless there is a clog in the system
No year or engine serial number so if I guess its a standard carb, open up the mixture screws a bit
No year or engine serial number so if I guess its a standard engine with points, check the gap

 

[97_Manta_Ray_CR]

I am sorry for not posting the engine year or serial number, It's a 97 mercruiser 3.0L/3.0LX I will have to get the serial number when I get home this afternoon, the engine does have a standard carb with an electric choke...

I believe my mixture screw is set correctly, the boat does run around 600-700 RPM's when at idle in the water
and my timing gap is set at +1 degree

 

[Rick Stephens]

I would not worry about thermostat. 140 is correct for a boat motor with open cooling system. The system operates under no pressure at all, so all hoses are soft.

Sounds like the carb needs adjusting or rebuilding. Not bad idea on a 10 year old boat.

I had my electric choke set to almost nothing when cold when I was running a 3.0 with a Mercarb. I live and boat at 2k+ altitude and never needed much choke. Once the element on an electric choke heats up you should see the choke plate all the way open and no longer in effect. Make sure that is so.

 

[97_Manta_Ray_CR]

Rick Thank you,

I rebuilt the carb 2 seasons ago and I have only ran non ethanol fuel in the boat ever since.

When the engine is cold the Choke plate is closed and then once the engine is warmed up it is open all the way.

I am in agreement with you that the 140 is good just wanted to check with you guys to see if I needed to worry or not

 

[Bt Doctur]

There is no "set position" .The mixture screw is set for the highest rpm at idle, opening it as much as necessary , the IDLE SPEED screw adjusts the idle rpm