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Where is our boat section???

Went to the lake yesterday with a friend to help troubleshoot an engine problem with his boat and he and I are disagreeing on the issue. It is a 97 model hurricane deck boat with a mercruiser 4.3 that he bought used back in the winter. He and I took it out back in early summer for a shakedown run and it felt like it had a slight miss to it but still had the old gas in it so we filled it up at the dock and put a can of sea foam in it. After that it ran good. He and his wife have taken it out a few times this summer and it was good at first but has started acting up again.

Couple weeks ago he drained all of the gas out of it and made sure the tank was clean and he also changed the oil. He got close to seven quarts out of it. The book says it should only have I believe 4.5. Anyway he and I take it out yesterday to see if the issue was fixed and it started off decent but as the day went on it got worse.

Starting off it would only run 3600 RPM but surge to 4000 for a second or two at a time. As the day went on it would only do 3200 and quit surging. It has a distinct miss to it and started running rougher the longer the day went on. It was so bad trying to load that it couldn't push itself on the trailer. One thing we noticed is that the oil after running about 20 minutes was grey and now overfull. It didn't look like it had water in it but rather gas. The fuel pump is electric mounted on the front right side below the water pump. I am not familiar with inboards but taking exhaust temperature checks when it was running all the right side was the same and all of the left side was the same but there was almost 40 degrees difference per side with the left being cooler. Does the fresh water come in on that side?

Anyway I keep saying he has a carburetor issue and he thinks ignition. Anyone else had an issue like this before?
 

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When i worked at the marina for some extra cash. i could not tell you how many carbs i had to rebuild from bad fuel. Units just sitting.. A lot of head gasket problems also. Work was consuming. Had to give it up. If by chance, pull the dist cap off and look at the reluctor ring and magnet in the dist. Rust was an issue also.
 

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Two things you can do,
One pull the coil wire and make sure the spark is will jump 3/8th of and inch and is a nice hot spark not a weak yellow one like an old lawn mower.
Second when it warm and fking up pull the spark arrestor/air cleaner off the carb and with it running under load make sure the fuel is coming out of both venturis equally in a nice pattern (not dribbling) make sure you wear eye protection and don't let your hand, dick or tie get caught up in the belt....

Me I am betting on the fuel system. Depending on the year the flexible line may not play well with ethanol and may now be in the filter or carb.
 

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Buddy just had the exact same issue with his. Ended up being a bad needle and seat that was flooding the engine then starving it. It stemmed from bad fuel line and filter. Start at the tank and replace all rubber hose, fuel filter and go ahead and throw a needle/seat and accelerater pump and maybe a float. Did that with his and now it hauls ass all day long. Thank you ethanol fuels
 

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mt brother in law's boat wold not come up on plane...i thought carb to. we changed the fuel/water filter and the four plugs. also found a loose spark plug wire at the distributer . ran great after that. i think the filter was the main problem
 

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we hadn't used our boat the past 3 years. Still had a full tank of 3yo gas with fuel stabilizer. Ran ok at the beginning then would not go past 2500rpm. Ran ok for an hour next time out, above 3200rpm, then would not go over 2200 again next couple times. Each time I put in more fresh fuel, Seafoam, cleaned the carb, changed fuel separater, oil and filter. Finally changed the plugs and thing was a completely different boat
 

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One thing we noticed is that the oil after running about 20 minutes was grey and now overfull. It didn't look like it had water in it but rather gas. The fuel pump is electric mounted on the front right side below the water pump. I am not familiar with inboards but taking exhaust temperature checks when it was running all the right side was the same and all of the left side was the same but there was almost 40 degrees difference per side with the left being cooler.
Left exhaust will be hotter than right by around 20*.

Oil level is higher? Check for water in the oil. Could have a crack/rotted exhaust manifold.

Pull plugs. Water on them?
 

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The 4.3 had a Mercruiser/ Rochester 2GC, "Mercarb",carburetor. Everything is the same except for the accelerator pump.
Get the right kit from a Mercruiser dealer. Hopefully you haven't leaned it out enough trying to fix it, to suck the valves.
 

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enrichener may be acting up or needle/seat, some 4.3's have a sensor in front of intake manifold that go to back of carb! I'd pull the plugs and check them also see if they have any black paint on them ,sometimes they never get changed! ,while there out crank the engine and see if any water comes out any of cylinders! new plugs,rotor/cap, separator filter!
you say it "was" running good so likely just needs some tlc!
 
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