1985 3.0 running poorly after ahile

My engine starts great and runs awesome for about 45 minutes then begins to sputter like it is not getting enough gas. I can shut it down and it will start right up. It will never stall, just run really poor. I have installed a fuel water separator and replaced the fuel filter in the carb. I try letting the boat sit for 15 to 20 minutes and start it up again but still sputters. I bring it home, hook it up to a hose and it runs perfectly. I take the boat out again and it will run great then the same thing. Boat operates at 130 degrees. So it is not overheating. Tried running boat with blower on at all times, no difference. I can not reproduce problem at home and have to run the boat for awhile to have it give me trouble. I have tried this five times so far. The good news is, At least I have fun for about 45 minutes and the boat never dies. The only thing that seem to make a difference was when I added to fuel water separator and replaced the filter in the carb with a screen type filter, the boat seem to have more power and overall just run stronger, but when it started to sputter again it was worse than ever, to the point I thought it was going to die, but made it back. Pulled the water separator off and poured the gas into a glass to see if there was any water and the gas, looked clean. Put the filter back on and started it up and ran perfect once again. I have not been out on the water since. What should I be looking for here? Why does my boat appear to work perfectly every time then sputter. Fuel pump starting to go and has problems when it gets hot? Coil? Help!!!!!

Either you have a fuel pump issue or a carb issue. One other place to look is the gas tank vent.......if it is clogged it will cause a vacuum to occur in the tank and cause a loss of fuel flow to carb. Shutting it down allows it to equalize the tank pressure.

Find the vent on the side or back of the boat and blow into it and make sure it is clear.

Thanks for the info. The vent was one of the first things I checked and that is good. This is more of a curiosity question, if the fuel pump or the carb is the problem, what is happening to them that is causing them to fail? I work on small engines and I am use to them either working or not. I am just thrown off how the engine can seem to work perfectly for a period of time then not. I assume it has something to do with them getting warm, I guess I am just wondering what is failing when they get hot. If I have to replace the fuel pump so be it, the carb I would have to rely on someone else to do that and I do not mind that either. Just want to make sure I have exhausted all other options before that.

P.S. I grew up in Northboro, lived near Juniper Hill golf course.

Not sure how to answer your question...when answering on here we can only suggest possibilities unless we absolutely know the answer.
If u want send me a personal message with your phone number and a time to call and we can discuss over the phone.

Mechanical diaphragm fuel pumps can work fine when cold...or warm, but as heat builds in the engine compartment, a worn/tired pump could begin to fail. Not saying that this is your problem, just trying to explain. Rick

That was what I was thinking too about the pump. So I pulled the pump apart to see if the diaphragm was breaking down and it look fine. Inside the pump was clean. Still could be the pump but I think I am going to look at other options too.

Just an update as to where I am at. I was lucky enough to receive some suggestions and was able to determine I have a fuel delivery problem. I figured I would start with the fuel tank, I pull the tank out and emptied out all the fuel and the tank was clean, tested the fuel for water and was clean also. The check valve worked and vent was clear. There was basically nothing in the tank that would clog anything. I currently have the engine hooked up to another fuel tank, just to verify the tank is not the problem. This leaves me to believe their is a good chance it is the fuel pump. Due to the fact the diaphragm is being exposed to hot oil and the fact the pump is really, really old I think when it gets to hot it just begins to lose pumping power. I think this is why when I installed a fuel water separator and when the problem started again, it was worse than ever. I think the weak pump now had to pull fuel through the extra filter and it was just to much. Funds are a little low right now, so after I test the boat, a new fuel pump may not be in the near future. Just have other projects right now and spent enough on the old boat this year. When I replace the pump, I will update how it went. Assuming the different tank does not change anything.

Good luck and keep us informed. Rick

Took the boat out this weekend and tried running on a different fuel tank and once again same problem, so it looks like a new fuel pump is next. As suggested, when the boat started to sputter, I tried pumping the throttle rapidly and the motor did pick up power.

Sounds like you're on the right track. I can tell you from recent, painful existence that low fuel pressure can cause all kinds of trouble.

Jeff