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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10593
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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Mercury I have a 50 hp mariner , approx year 1990, 3 cylinder

Customer Question

I have a 50 hp mariner , approx year 1990, 3 cylinder 2 stroke.
I was out fishing and it suddenly stopped. No coughing or spluttering as to indicate fuel starvation. I believe it to be an electrical fault, perhaps a safety cut out or a problem with the fuel pump. The engine turns over well and I am getting 3 good sparks at the plugs. (all in good condition ), I have checked for any obvious loose wire, bad earths, but cannot find a problem.The engine turns over well ( electric start ) but will not fire.
Your help would be much appreciated.
I have previously had help from Captain Dave.

Kind Regards,

Submitted: 5 years ago.
Category: Boat
Expert:  Tan replied 5 years ago.

Hi my name isXXXXX will assist you.

Do a compression and spark test on all cylinders to eliminate these as a cause for your issue. The spark should jump a 7/16" gap on a spark tester and the compression should be 100+ psi with no more than 15% difference between cylinders. If these check good we can move on to the fuel system. If there is a spark or compression problem post back with findings.

Squeeze the primer bulb till firm, if bulb will not get firm we have a bad fuel pump or a flooding carburetor. When you remove the spark plugs check if they are wet with fuel. Check the fuel in the carburetors for contamination or water. There is a drain plug # XXXXX on the side of each carburetor remove the plug check for contamination, if anything but fuel comes out of the carb the carburetors need to be removed disassembled, cleaned and carb kits installed. If you find just water you must pump the fuel tank change all filters and drain the carbs. Once you have removed the water drained the carbs try starting the engine. Post back with questions. Diagram of 50 (3 CYL.) Mercury Outboard (NNN) NNN-NNNNTHRU(NNN) NNN-NNNNCARBURETOR (WME-22-22B-23-24-35) Diagram and Parts

Customer: replied 5 years ago.

Many thanks , I cannot check the engine til tommorow as I,m off to work.


Will let you know a.s.a.p,





Expert:  Tan replied 5 years ago.
OK, I'll be available.

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