Need some help with two items........

Just returned from our Lake Powell trip (had a blast) and had a issue with the boat and another with the trailer brakes.

The boat first, I think I'm getting water into the fuel tank somehow? The boat would run great when first put into the water each day. If you let it sit (not running) for some time then go to start it, it would crank, start, but not stay running and even die when you gave it some throttle. The way I was getting it to run was emptying the fuel and water separator filter, filling it with new fuel from the gas tank and reinstalling. Once I did that it would fire up and run like a champ.

I think the water is coming in from the fuel tank vent on the side of the boat, it is mounted kind of low in my opinion. This winter I replaced the fuel tank vent, placed the 90 degree elbow straight up and put a loop in the fuel vent hose to act as a trap. Does anybody have any suggestions? Is there a specific vent out there to help with this or can you place a one-way-check valve in-line to prevent water coming in?

For the trailer brakes, whenever I would start to come to a complete stop the trailer brakes (surge brakes) would lock then release causing a jerking motion. But it would only do it just as I was making a complete stop. What would be causing this and how do I fix it?

Thanks for your help.........

I am guessing it is a fuel pump problem and your filling the canister overcomes the low pressure pump going out (which I think fills the canister) so that the high pressure pump can work and siphon effect can overcome week low pressure pump.

But like I said I am guessing.

My guess is vapor lock or the loop you put in your vent has gas or water at the bottom not letting the tank breathe and thus pulling a vacuum in the tank when trying to run. Since you've been pulling the water separator out and refilling with fresh fuel, have you actually dumped what was in it into a clear jar to see if water is actually in the fuel to begin with? Your gas may be fine and you're not really getting to the root problem. Check your gas for water first and undo the loop in the fuel vent line. They need to breathe.

To back up some I had the same problem last year. Took it to my mechanic and he found water in the tank and in the fuel and water separator, he even saved the fuel from both and showed me the separation. That's way I changed out my fuel tank vent, and put the loop in the hose. Figured it was coming in from there, I also replaced my fuel filler just to rule out water coming in that way. After he drained the tank and replaced the fuel filter, I filled the tank with new fuel replaced the fuel vent items as stated above and it has ran great without any problems for 3 trips, until now!

I pulled the fuel vent hose and found no fuel or water in the hose or the loop, but it has been siting for a few days (on the drive home). Just pulled the fuel filter and dumped it in to a clear glass jar and so far do not see any separation?

All the fuel related parts were changed out about two years ago, including the fuel pump. It is a 2000 Mercury MerCruiser 350 MAG MPI and correct me if I'm wrong, but I don't believe it has a low pressure fuel pump just a high pressure pump.

Have you been running with your blower on? If not, you need to. Sounds like vapor lock. Does opening the engine hatch and letting the engine bay cool down, does it start up and run fine? Ive got the same engine and I had it do the same thing your experiencing once this past week. First time in a long time that ive had that come up. I put it in neutral and gave it wide open throttle to try and push the air out of the lines while turning it over until it was running and cleared up. No problems after that. If it was water, you would have seen it. Most likely when you pulled the fuel filter off, you let the air in the lines out and thats why it would start and run after that. If it was water, it usually will idle fine, but will cut in and out in the upper rpms.

I have been using the blower, but probably not as much as I should be. There was a few times where I turned it on and forgot to turn it off and ran the boat for a while with it on and come to think of it I did not have any problems that day. Also that same day I would start the boat every half hour or so and let it idle when anchored to try and prevent this problem and I was good all day by doing that.

Have not tried opening the engine hatch, I will try that next time. Also one day when it would crank, start, but not stay running I feathered the throttle for a while to keep it running. It seemed like it cleared itself and ran fine after that. Maybe I'm dealing with a vapor lock issues like you said. Also thinking about it some more, a lot of these problems started happening after I had the upholstery and carpet replaced. Not sure if the new upholstery and foam on the engine hatch, along with the new carpet (which is different and thicker then what was there before) has anything to do with holding in the heat more? I found that Mercury MeCruiser has a service bulletin out about vapor locking. They also list some kit part numbers to help avoid it. Kits include, a check valve kit, electric Anti-Siphon valve kit, and a fuel pump kit? Not sure if they are worth the try.

Thanks for the help!