Cutting out and losing RPM

[Betty the Boat]

I finally got my boat put together after rebuilding the carburetor, changing the fuel/water filter, and changing the timing belt. I took it out on the water today and the boat ran beautifully! I would say that the boat never ran so good! However, after about 45 minutes on the water the boat starting cutting out and losing RPMs. It seemed to do this during rapid acceleration, and pushing speed from 3,500 RPM and 4,500 RPM. It is very intermittent. But, definitely started getting worse as the day wore on. It is not a problem at all in low RPM and idle.
Thoughts:???
Bad Fuel? - I have been running Non-Ethanol Fuel and plenty of Sea Foam for the past 2 tank fills, and when I changed the fuel/water filter the gas looked pretty good? (clear and smelled good)
Fuel Pump? I pulled the fuel line from the carburetor/anti-siphon valve and cranked it over and fuel shot out. But, I'm just not sure how much or how fast it should have been coming out.
I have an 1989 OMC Cobra 2.3L
Thank you for any ideas

 

[jerryjerry05]

Maybe it's running hot?

 

[Scott Danforth]

could be dirt in the carb
could be fuel system
could be plugged vent line on tank

 

[Betty the Boat]

I am 99.9% sure it is not dirt in the carb.
Pretty sure it is not running hot. (new water pump repair kit and temperature looked good on the gauges)
However, I am very interested in "plugged vent line on tank"! Please explain more. Any trouble shooting I can do to see if the line on tank is vented properly?
Also, when you say "fuel system" , are you speaking mainly of the fuel pump?

I also wanted to mention that I filled the tank just prior to putting the boat in yesterday with Non-Ethanol fuel.
Also, the boat seemed to not have as much trouble when the back cover was off and the air filter/arrestor was off.

 

[Bondo]

Also, when you say "fuel system" , are you speaking mainly of the fuel pump?

Ayuh,.... Welcome Aboard,... The "Fuel System" includes the tank vent, the tank, the tank's outlet fittin', the fuel lines, the fuel filter, the fuel pump, the carb, 'n it's choke,....

 

[Snoopy11]

Had similar issue on my honda 4 stroke 75hp. Did all checks ended up being a faulty thermostat. Its another option for your checklist...

 

[Betty the Boat]

From what I have read on the internet and in these threads, I am going to start with the Fuel Tank Vent. Does anyone know how the fuel tank on the Bayliner Capri OMC Cobra 2.3 liter is vented? Also, where is the vent? Is this a replaceable part? How do I diagnose?
I would also like to replace the anti-syphon valve: Where would I find this?
Lastly, I would like to check the to see if something is blocking or clogging the fuel coming out of the tank. Any ideas?? Is there some sort of screen that I can pull and clean out? If so, where would it be?
As you can tell, I am completely challenged when it comes to gasoline engine mechanics! However, I love to learn. So, any advice is greatly appreciated!!!!

 

[bruceb58]

You can run without the gas cap on to see if that helps. If it does, you have a clogged vent

You can also run the engine on a portable tank to isolate the fuel tank out of the equation.