1997 Doral 300 SC twin 5.7 mercruiser

[acadian2022]

Good morning everyone. I'm posting this for a friend having issues with one of his engine. So last year my friend went to fuel his boat and turnout the o'ring gasket to his gas cap feel out without him noticing and for several days it rain and I mean it rain a lot next thing you know apparently water got into his gas tank and ever since one of the 2 engine will turnover but wont start. he got the tank emptied full flush of both engine, new gas and only one of 2 engine will start and the other turnover but wont start. he brought the boat to an engine marine shop and they said 2 cylinder don't have compression we will review that this morning to confirm if that is the case. as a starting point can anyone please provide basic check / test of parts to try and start that engine Thank you all have a great day.

 

[dubs283]

Verify the water separating fuel filter is full and void of anything but fresh fuel.

Verify the carburetor/fuel injectors are supplying fuel to the engine.

Verify the ignition system is sound through a visual inspection of the components and with a spark test at the coil/plugs

Verify the cylinder compression with a tester. If no tester is available a backyard method is to compare the noise the engine makes when turning over to a known sound running engine. If the engine with suspected low compression on two cylinders sounds like there is a consistent "skip" in the noise of turning it over there could definitely be severely low compression on one or more cylinders

 

[Bondo]

he brought the boat to an engine marine shop and they said 2 cylinder don't have compression we will review that this morning to confirm if that is the case.

Ayuh,..... Confirm this, then do a leak-down test to see where the compression is being lost,.....
That can give you an idea of whether it's burnt valves, or worse,....

 

[Scott Danforth]

I would run the motors off a good fuel source like a 3 gallon outboard tank

Verify compression

 

[crazy charlie]

1st thing I would do is remove fuel water sep and empty into a jar .Fill to the brim with fresh fuel and try cranking it up.Charlie

 

[crazy charlie]

1st thing I would do is remove fuel water sep and empty into a jar .Fill to the brim with fresh fuel and try cranking it up.Charlie

Fill separator to the brim with fresh fuel and rei stall.

 

[acadian2022]

Good morning all thank you all for the suggestions all is noted and will try everything that was pointed out. I do have a digital compression tester on the to do list to check all cylinder compression. will keep you all updated have a great day.