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#1
IP: 204.136.203.146
04-29-2019, 12:22 PM
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1984 Mercrusier 140 Help
I have a 1984 Mercruiser 140 3.0 that I am having a issue with. So the engine will start and run fine on a hose, sounds good no knocking or any out of the ordinary sounds. I can give give it gas and it will do just fine. Once I put it in gear and give it gas it will spit and sputter but will accelerate. Once I put it in the water I can start it and it fires right up and sounds great. Once I put it in gear and try to accelerate it falls on its face back fires thru the carburetor and dies. It will start right back up and still idle great. It will only die when accelerating under a load. So far we have checked the fuel pump and it is fine, replaced the ignition coil, points, distributor cap, rotor, spark plugs, Checked compression (Good), Set timing, fuel filter, changed gas out (even have it hooked to external tank), new carb, set bowl level to the book. Not sure where else to turn. Any help would be appreciated....
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#2
IP: 24.152.132.140
04-29-2019, 04:17 PM
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Based on your symptom set I would double check the timing. It sounds to me like it is way advanced to start with and only gets worse as the RPM increases due to whatever advance mechanism that engine has. The firing back through the carb tells me you are getting ignition with intake valves open.
__________________
Neil 1977 Catalina 30 San Pedro, California prior boats 1987 Westsail 32, 1970 Catalina 22 Had my hands in a few others
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#3
IP: 137.200.32.54
04-29-2019, 04:33 PM
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I was thinking also the accelerator pump????
BTW - those engines are HUGELY prone to leak water into the oil. Mine got so bad I would put a container under the engine and drain about 3-4 quarts of water before starting it  Check the oil EVERY day and watch for it going up. If you don't do that and there is water in there, starting the engine mixes the water and the oil to bad effect.
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#4
IP: 134.41.89.244
04-29-2019, 10:41 PM
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I haven't worked on a merc but my own Suzuki had a similar problem when I first got it. Couldn't find the problem for the longest while...turned out to be a fuel filter installed backwards. Turned that around once I saw the arrow in the wrong direction and it was fine.
__________________
Mo "Odyssey" 1976 C&C 30 MKI The pessimist complains about the wind. The optimist expects it to change. The realist adjusts the sails. ...Sir William Arthur Ward.
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#6
IP: 70.185.132.18
04-30-2019, 10:22 AM
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$0.02 Worth
Quote:
TRUE GRIT
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#8
IP: 204.136.203.146
05-01-2019, 09:46 AM
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So should timing be checked and adjusted while its under a load or at idle on the hose? He said the timing is set and while boat it at a idle on the hose it sounds great. You can accelerate while in neutral and when you put it in gear it idle fine but soon as you give it gas it spits and sputters and dies if you give a lot of gas. On the hose while in gear if you ease into it slowly it will accelerate but if you go to fast it dies and back fire thru the carb. While in the water it will start and idle fine and accelerate in neutral but when you put it in gear and give in any gas at all it will die and back fire thru carb. If the firing order is off will it run good at a idle?
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#10
IP: 70.185.132.167
05-01-2019, 11:38 AM
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If the engine has a spark advance ( I bet it does but I don't know the details) it is probably not advancing off idle setting because it is somehow not functioning correctly.
TRUE GRIT
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