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4.3L V6 Mercruiser - Will not run, water in fuel, help troubleshooting!

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bmyohn

New member
Hi everyone,
I have a Crownline w/ a 4.3L V6 Mercruiser with a Thunderbolt IV ignition.

It’s always taken a bit of throttle to get the boat to run,but now I can’t get the boat to stay running at all. It turns over, no problem but wont run.

I can get the boat to fire using starting fluid but it won’tstay running. This first made me think that the boat had spark, but wasn’tgetting fuel. So, I pulled the fuel lineoff and checked that there was fuel at least getting to the carb and there wasfuel pressure there.

I noticed that the gas coming out of the fuel line didn’tsmell great, so I pulled the fuel-water separator thinking there could be waterin the gas or the fuel was dirty.

I poured the contents of the separator into a dry waterbottle and easily 60% of the content was water and the rest of the content wasclean fuel.

I drained the entire fuel tank until it was empty andreplaced the fuel water separator. I tried starting the boat and had the sameissue. It would only run on starting fluid.

I next thought that the spark plugs might be fouled from thewater so I replaced them all with brank new NGK. Same problem, it will only runoff starting fluid so I’m still thinking that it’s not getting fuel.
What other things could I be missing? What would cause theboat to not be getting fuel like it should?
Any help troubleshooting would be greatly appreciated!

Recap:

  • Drained fuel
  • Replaced fuel-water separator
  • Checked for fuel pressure at gas line into carb
  • Runs off starting fluid
  • Replaced spark plugs
 
Ditto you sucked all the crud & water thru entire fuel system and it all stopped in carb.Flush entire system from inside of tank to carb, lines, fuel pump,everything then go thru carb. thoroughly
 
Jets will need to be cleaned out mechanically. I've not had any luck with an air hose. My go to tool these days to clean carb jets is a 4" piece of multi strand electrical wire ( 22 g or larger). I strip about half of it. I use the still insulated piece of the wire as a handle and then I peel back one strand at a time until the wire is small enough to enter the jet and clean it out. Gets small bits of shellac out that an air hose does not seem to due to rotorooter action.. It still takes a bit of blowing and careful banging on a wood surface to get the crap out of some of the passages, especially the ones in the venturi cluster of a mercarb.

Better buy new gaskets first.
 
Last edited:
sandkicker said:
Jets will need to be cleaned out mechanically. I've not had any luck with an air hose. My go to tool these days to clean carb jets is a 4" piece of multi strand electrical wire ( 22 g or larger). I strip about half of it. I use the still insulated piece of the wire as a handle and then I peel back one strand at a time until the wire is small enough to enter the jet and clean it out. Gets small bits of shellac out that an air hose does not seem to due to rotorooter action.. It still takes a bit of blowing and careful banging on a wood surface to get the crap out of some of the passages, especially the ones in the venturi cluster of a mercarb.

Better buy new gaskets first.
Click to expand...

You should invest in a small ultrasonic tank. Cook your carbs for a few hours. Takes everything off including the paint.
 
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