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1998 7.4 L mercruiser engine miss

C

charlie young

New member
Hi i wonder can anyone help me, i have a 1998 7.4 l mercruiser which was ran all last year without missing a beat, over the winter the only thing done to her was a new set of plugs.
The first day out on her she ran at tickover fine, when the engine was warmed up i accelerated and she took the speed and went on the plane great, i then stopped to pick people up and when i tried to accelerate again she started to miss, be very lumpy and cut out the only way i could describe it was as if it was dirty petrol ! ,the very next day i put more petrol in her and she didnt miss a beat,today i went to use her put more petrol in , warmed her up and she done the same thing ,missing with the odd back fire,running lumpy and cutting out i noticed after i dropped anchor and left it for a while she didnt seem as bad ,we took the fuel filter off and there was no water in there ,when i nursed her back to berth ,engaged neutral and revved her she took the rev but seemed lumpy ,does anyone have any ideas? one thing i noticed before this happened was the the boat seemed to be idling about 1600 rpm turning her off and on again seemed to cure it , im wondering is this linked in any way with the lumpyness and cutting out
sorry for being so long winded !!!
 
Welcome aboard !

First all the plug wires seated fully ? Check them again. Under your cap is dry ?


I would, clean the filter that is in the fitting at the carb, you say fuel water sep is clean, then pull the fuel pickup tube at the tank, check the valve and the screen on the bottom the the tube.

Then i would suck all the gunk and water off the bottom of the tank and close it up and run the boat again. Now you know the system is clean.

Say it's not fixed and the timing is good, i would pull the plugs and read them. Maybe your running lean.

I have to ask what else does the motor do ex: Overheat maybe running hotter then normal ????
 
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So it starts running bad after about 10 or 15 minutes? I had that problem last year and it turned out to be water in the fuel tank. After about 10 minutes the water gets churned up and sucked into the fuel line. You have to somehow get the tank completely cleaned out.
 
Ayuh,... Sounds like it could stand a Full, 'n Complete Tune Up, 'n Service....
possibly a carb Rebuild...
 
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