I have a 1993 Maxum with a 3.0L Mercruiser stern drive. It starts and idles just fine. However, when I increase the throttle, it sputters and kills at about 3,000 RPM. I have replaced the fuel filter. I just had the carb rebuilt a year ago. What else can I check? It ran great in late May. I haven't run it since then other than in my driveway with a hose attachment which is where I am running into the issue with what appears to be fuel starvation.

How old is the fuel in the tank? Old fuel can act like that. Could be weak spark or bad fuel pump.

Is your filter a water seperating one?

How long since cap, rotor plugs and points were changed?

I filled the tank in May when I took it out for Memorial Day. The tank was mostly gone and then sat until August 2nd when I started the boat up in my driveway with a hose adapter, so that would have been sitting for just over two months.

I replaced the fuel filter, but it does not have a water separating filter. The boat is a 1993 model that was well kept by the previous owner. I had the carb rebuilt last year, but I don't know how long it has been since the cap, rotor plugs and points were changed.

I would add some fresh fuel to it and get a water seperating fuel filter for starters. And the basic tune up would be next on the list. All those things should probably be done anyway so no money wasted if they do not solve the problem.

Another area to look at would be the fuel pump and the anti syphon valve at the fuel tank. Sometimes those valves can stick and starve the engine for fuel.

So after replacing the fuel filter and running it for a while in the driveway, I decided to take it out on the lake and run it for a bit hoping to flush things out. In the driveway it was starting and idling great and running up to nearly 2,000 RPM without a problem. Well, I took it to the lake and the thing wouldn't even start. I could smell the gas fumes and eventually flooded it. One thing about the fuel filter. The filter I pulled out of the unit was a ceramic bowl type filter. The one they sold me at the boat shop which was listed for my engine was a simple paper-based filter.

Is there a way I can check the fuel pump? I have the Seloc manual for my model Mercruiser, and I can't find anyting about the anti-siphon valve other than a definition of what it is. I'm not sure where it is exactly.

The anti-syphen valve is in the fuel tank pickup but it does not sound like fuel is your problem since you stated that you flooded it. Sounds more like weak spark or weak gas.

It does not take much power to run a motor in neutral. If you have ever put on the gas when the light turned green and forgot that you had put your car in neutral you know how easily it goes to redline. Similarly, weak gas or spark will run fine on the trailer where there is no resistance but in the water it's a different story.

I would change the points and condenser, cap, rotor and plugs before I did anything else.

Also, you said you had the carb rebuilt last year so I would check to see if the choke is opening and closing properly.

Thanks. I'll change those things out and see how she goes. I appreciate it.

Hope it fixes your problem. If not, you haven't wasted any $$$ since those things should be done every 3-4 years anyway.