Mercruiser 5.7 problem - What should I check

[wellcraft12]

So I took the boat out yesterday and it ran great all day. On the way back in we were in a long no wake zone and i had the boat with the throttle at its lowest setting crusing along. I start hear a loud knocking sounding like it is coming from the drive line and the engine starts running rough then dies. I put the boat out of gear and it starts up and runs for a few seconds and dies again, acting like its out of gas. At this point i cannot get the boat to start again. I let the boat sit for 10 minutes and it fires up and runs. I put it in gear and go about a half mile and it happens again. VA was already on the way and towed us the rest of way to the dock.

Once i got the boat on the trailer i proceed to flush the engine with fresh water and it runs for about 5 minutes and dies again. I cannot get it to start again and then i start thinking its acting like its getting flooded. I open the egine cover and it stinks of gas. No visable leaks or anything.

Any ideas on what i should check?

[mattmuttsmithx]

What type of fuel system do you have? Is it fuel injected or carbed?

If it is carbed it sounds like a fuel pump issue or possibly a gummed up carb.

If it is fuel injected it could be a fuel pump or a fuel pump relay or broken fuel rail line or something similar.

Give a little more info on what the engine actually is the 5.7 is the most popular engine out there.

[wellcraft12]

Sorry i lef that out.

Its a GM engine, carbureted.

[fishingfun]

I'd check to make sure its not a leak in a line. If not good chance the float is getting stuck.

[Local Motion]

Get a carb rebuild kit.
I used to do it every other year when I ran a carb.
Mostly it is just cleaning.
You would be surprised how much salt accumulates around the main jet to cause problems, just from salty air. That is probably all it is, a good cleaning.

[Stim]

Check your oil to see if it is overfilled too. If a fuel system problem gas can get in crankcase, NOT GOOD.
I/O's need to check oil frequently for over full, can be water or gas. Either can destroy the engine.

[wellcraft12]

Thanks Stim, Its just straight inboard. I had checked the oil before we went out and it was not overfull but did not check when we got back.

[billinstuart]

Have you checked your fuel filter? Gas tank vent plugged?

The LAST thing you want are gasoline fumes in your bilge!!! If you are having these problems, smell gas, and don't know what you're doing, HIRE a professional.

DO NOT crank or start your engine with gas fumes in the bilge!!!!

[ziess21]

Check for water in the fuel as well.

[baitkiller]

Start it or crank it over if it wont start then turn it off and pull the flam arrestor quickly. Open the throttles and look down the throats with a flashlight (not your Zippo) you will likely see gas running out of the little holes and across the plates. This would indicate a fouled float needle and seat.

time. Easy peasy lemon squeezy.

[wellcraft12]

Thanks guy, I really appreciate the suggestions!

[baypro21]

I would get a 6 gallon tank and run the engine off it with fresh gas to see if that makes a differance. I got some gas in my water 2 years ago and it ran fine out to 16 miles before it started running rough and eventually cut out completely.