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Old 11-14-2018, 01:03 AM   #1
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Default SCR 2900 7.4 Brave 3 single no WOT

Hi everyone. New to boating and forum. Problem is not getting boat to plain out as only able to reach 12-14 mph at 3000-3200 rpm. Usually 28-30 mph at 4400-4600 rpm. Started in middle of season.No noises or smells. otherwise runs fine!!. Marina pulled boat/cleaned bottom and engine(minimal growth) and took boat out for a test.Problem still present. Could not diag. any electrical prob. or codes. They said they are not savy with Mercruiser engines. I tried Sea Foam.No luck.I used boat till end of season. Again no other problems or alarms Boat is stored at another marina where they specialize in Mercruisers and will be a winter or early spring project.Any thoughts?
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Old 11-14-2018, 02:16 AM   #2
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Welcome aboard

Not fimilar with mercruiserís? Most popular I/O in northamerica.

What year is the boat?

Did you have the props checked? A small amount of damage may not be visible to the eye but make a big difference.

While there are no codes I would perform a compression test of the cylinders to make sure they are all healthy. You can have a bad cylinder and other than a loss of power not know it.

Potential issue with low fuel pressure, either regulator or cool fuel clogged by inter paint chip which is a know issue on some years.
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Old 11-15-2018, 04:27 PM   #3
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Thank you for replying. Boat is 2001, approx 345 hrs on engine and props are fine.Have owned boat for four seasons and compression test done each year and all ok.I hope it is an ea$y fix....once problem is diagnosed.
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Old 11-15-2018, 11:02 PM   #4
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Jagdad,
Have you checked the distributor cap for cracks or moisture?
Is it carb or FI? If carb, when is last time you had carb rebuilt? Check the fuel filter screen going into the carb.
Have you checked resistance of spark plug wires? An easy check is to run a screwdriver down the length of each wire with about a half inch spacing. If you see sparks jump to the screwdriver then you need new wires. I can look up the resistance specs if you want to check them with a multimeter.
Pour contents of fuel/water separator in a jar to see if you're getting water in the fuel. Let it set for a while after pouring it in to give it time to separate.
Take a look at the spark plugs. See if anything looks off like wet tips or sooty.
Any chance you have a clogged exhaust?
Any odd noises or smells?
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Old 11-16-2018, 06:07 PM   #5
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Thank you. New plugs and wires this spring.EFI.Boat is stored for winter.I will await solution and will post same.
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