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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11052
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1982 70 hp mercury and a 1985 25 hp mercury. neither

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I have a 1982 70 hp mercury and a 1985 25 hp mercury. neither have been started in 6 or 7 years. Is there a procedure to start these engines? Or should I write them off and buy a newer model

Hello. My name is XXXXX XXXXX I will be assisting you today.


The first steps are to do a compression and spark test. The compression must be 100+ psi with no more than 15% difference between cylinders. The spark must jump a 7/16" gap on a spark tester.

If these check good and the engine doesn't start remove the carburetors, disassemble, clean and install carb kits. Rebuild the fuel pump as it will be dried up also.


Once started remove the gear case and replace water pump with a water pump kit.


Now this is the procedure we go through on an engine that has been sitting unused for an extended period of time.


Be sure to use fresh fuel as the fuel in the gas tank with be bad and will need to be removed from the tank.


Post back with questions and concerns before rating please.

Customer: replied 3 years ago.

Thank You Tan, I assume that if the compression and spark are not up to specks its a lost cause or a rebuild?

Correct but depending on what you find will determine this. If you have a spark issue it can be repaired. The compression is the only thing that could be major. Now if the compression is low on all cylinders there is a good chance you could just have some sticking rings which we can help with power tuner.


So let me know what you find and we can determine what needs to be done.

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