Mercruiser 3.0lx wot issues

Brokeboater95

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Joined
Aug 17, 2017
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2
Hey everyone. I recently acquired a 95 citation 1900cuddy. 3.0lx powered and I'm having issues. Don't know maintenance history at all. Cleaned carb when got it, ran great for a while then started blowing black smoke. July 4th this year the carb fell off the throttle plate and its been down hill since. Ended up doing plugs, wires, cap, rotor, re built carb several times and eventually a head gasket and set timing. Boat runs like a champ on the trailer with muffs.. But in the water, runs rough still, and at wot it falls all over itself. Boat seems to have been cobbed up over time.. Has inline fuel filters, which I will change this weekend. Any thoughts on why it would stumble all over itself. Sounds like its starving for fuel at wot. Boat was great in the beginning.. Would hit 40-41 mph.. Now... I'm lucky I can hit 35 with a struggle.. Thoughts?? I'm new to boating so I'm clueless. I am a car mechanic of it helps.
 

Scott06

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Apr 20, 2014
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5,542
A couple of questions you mention black smoke which implies rich, but then say it's starving for fuel? Did the carb rebuilds cure the rich running? What do you mean by " the carb fell off the throttle plate"?

If it's running rich check that rupture line from fuel pump doesn't have gas in it. This is the clear yellowis hose from fuel pump to carb, if fuel pump diaphragm breaks this dumps fuel into the carb rather than into th bilge.

When changing the fuel filters dump the contents into a clear container, boats often get crud or moisture into the gas. If crud laid eyes a complete cleaning of fuel system is needed. Other items that can starve for fuel are anti siphon valve on fuel tank, crud in pickup tube, clogged tank vent, deteriorated Fuel lines, weak fuel pump.
 

Brokeboater95

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Joined
Aug 17, 2017
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2
Black smoke at first. Yes.. So running very rich I'm assuming.. Then the carb fell off.. There's a throttle plate screwed to the bottom of The carb with 3 screws.. Then the while unit bolts to the intake with 4 nuts/studs. I have cured the black smoke problem after doing all the work.. But now it seems like it may be starving for fuel. I recently realized I never replaced the power valve in the carb.. I'm not even sure if I have the proper carb on my boat. It has cheap inline clear plastic fuel filters.. One before the fuel pump, one just before entering the carb, they don't looks so clean.. I also am going to change the filter in the pump itself. There wasn't a filter in the inlet in the carb itself either. The yellow tube is clean and clear.. O replaced that as well.. Looked crappy when I was doing the head gasket repair. Everything was torqued to specs by the book and timed by the book to spec as well. Carb cover said to set at 1degree btdc.. That's where she is.
 

fishrdan

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Joined
Jan 25, 2008
Messages
6,989
Install a water separating fuel filter before the fuel pump and ditch the (non-marine) in-line fuel filters. Since you say the engine is cobbled, use A1 marine fuel hose, it's burn rated unlike the "cobbled up stuff" that may be on the engine now.

1* BTDC, sounds like EST (electronic) ignition. Are you jumpering the distributor wires and putting the ignition into base timing mode, while timing the engine. What does the engine's timing go to when the timing shunt it removed? Initial timing should be 10-12* at 650-750rpm when the shunt is removed. Total timing is around 26-28* at 3000RPM.

How does the compression look?

Do you have an OEM Mercruiser manual for your engine? They are downloadable online.
 

Scott06

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Apr 20, 2014
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5,542
Someone thought there was a fuel issue and added not one but two fuel filters. The factory filter is in a bowl under the fuel pump, would recommend replacing the fuel lines in and out of the fuel pump with the correct A1 hose, replace the factory fuel filter in the fuel pump and ditch the added filters. Make sure timing is right and ignition components are in good order, test run it off a separate tank of fresh gas. If problems go away you need to take apart the entire fuel system clean and reinstall. If problems still are the same look at other components like ignition.
 

alldodge

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Staff member
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Mar 8, 2009
Messages
40,581
Being a 3.0lx and 95 model I'm seeing timing at 1 BTDC
What is your serial number?
Do you have EST or DDIS distributer?
 
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