Mercruiser 3.0 1987 engine not running well after warmed up

alpha-newbe

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Joined
May 27, 2025
Messages
17
Engine idles fine and will run smoothly at lower rpm in neutral and in gear. After running smoothly on the lake for 15 min or so at 3500 rpm then running for 15 min at 1000 rpm smoothly all is good. Then i go to running at 3500 rpm again and it runs rough so i back the rpm's down to 1500 again and it runs smooth. So then i just take if back off the lake because it is not running well.
 

alldodge

Moderator
Staff member
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Mar 8, 2009
Messages
42,947
Might be a fuel pressure issue (pump or fuel lines) but when was the last time the carb was cleaned?

Have you checked the points and the dwell
 

alpha-newbe

Cadet
Joined
May 27, 2025
Messages
17
Might be a fuel pressure issue (pump or fuel lines) but when was the last time the carb was cleaned?

Have you checked the points and the dwell
Thank you alldoge! I currently have a carb rebuild kit and will plan to start there. Then fuel line checking and main fuel filter at base of engine. Already changed the small filter screen at the fuel inlet to carb.
 

alpha-newbe

Cadet
Joined
May 27, 2025
Messages
17
Thank you alldoge! I currently have a carb rebuild kit and will plan to start there. Then fuel line checking and main fuel filter at base of engine. Already changed the small filter screen at the fuel inlet to carb.
New distributor cap, plugs, wires, condensor, and new rotor arm with gap set to Merc spec., ignition coil, and starter solenoid.
 
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