Boat performance problem

Okay, kind of a strange issue. I had problems with the boat a while back where it was bogging down under load.

I pulled the throttle body out and checked the fuel pressure regulator and the diaphragm was covered with crap, so I replaced it. Problem is, I'm still having the same problem.

I've taken it apart a couple of times to check it out. Every time I do, the boat runs fine for about an hour or so and then starts losing power again. More specifically, out of the hole, it'll bog down and then kind of catch and pick up. It will gradually get worse until the boat will barely idle at any throttle setting. It's almost like there's some leak somewhere that's causing a gradual loss of fuel pressure. Does that sound plausible?

I've got fresh gas in the tank and I've added fuel injector cleaner. I'll probably be taking it to the mechanic, but figured I'd get some input on possible causes here first.

Check your vent line.

might be a sign of vapor lock? it sounds like it is obstructiing the flow of fuel to the engine, caused by the formation of bubbles in the gasoline as a result of overheating. you might check one of three things: first, your in-tank fuel pump or pressure regulator may (still) be a faulty component. you should focus on the pressure regulator first, because if it fails it would not allow fuel to return properly to the fuel tank. This could cause the vapor lock problem because it would literally boil any stagnate or stationary fuel before it gets to the injector. Have an engine mechanic confirm that the pressure regulator is within factory specifications, or just replace it. Second, the in-tank fuel pump itself may be the problem. That in-tank pump is of a type that is highly susceptible to damage from contamination. if you had to clean "gunk" off of the pressure regulator then you need to look at the fuel filter, as it is probably needs replacing too.. losing power could be a result of the fuel pump beginning to wear making its output become weaker. If the pump is weak, the engine will lose power after the pump has warmed up. again, have a technician confirm that the output pressure of the pump is within factory specs, especially after the engine has had time to warm up with the scenario's you have mentioned. and thirdly, the final possibility is that the fuel lines may be heated beyond design parameters. this typically happens when the fuel lines and exhaust manifold follow each other too closely along the block or near superheated components of your engine and/or engine compartment.. hope this helps and good luck! let us know what you find out..

your fuel filter first. also the fuel pump on most early boats are just a auto pump. On a car they are submurged in fuel and that keeps them cool and luberciated. On a boat aplication they are not submurged and get hot. I know of a couple of mercruser models that had a recall on the fuel pump that involved putting in a fuel pump cooler witch is a box that has fresh water lines in it that has the pump mounted in the center.
I would check your cap and rotor for moisture and wires for cracks. The spark will take the least path of resistance and will under load and idle leak out or misfire. But more common is your fuel pump. I would replace it and your fuel filter its not that expensive. Remove your pump go to a Napa and ask for a pump for a 94 Chevrolet 350 throtle body inj truck. You'll see the only difference is one is painted and the other is not. You dont have to worry about marine grade due to the fact that this pump is designed to run inside a fuel tank so sparking is not a issue.
As far as the gunk in the engine. Get a can of berrymans fuel system cleaner. Pull of a vac line, start your boat and submurge the line in the can untill just about staling. Then poor the rest in the tank. Most likely cause for sluge is in frequent oil changes.
Also as mentioned pull of the vent line from the tank and blow it out. They get full of water and their is not enough psi form the tank its self to clear it.

Had the same problem. Ended up being junk in the gas tank. I replaced the gas tank (including pickup with a fine screen on it, and everything worked. I replaced the carb, ignition system, all fuel and vent lines, fuel pump before the gas tank. Lots of cash.

Well, it definitely wasn't the vent line.

Guess junk in the gas tank is a possibility, since it would gradually lose fuel pressure. I'll check that next since it's the easiest of the proposed fixes.