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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 11076
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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I have a 1961 merc 60 6 hp motor runs fine at idle up to half

Customer Question

I have a 1961 merc 60 6 hp motor runs fine at idle up to half throttle. At full throttle will die like it's running out of gas. Take cowling off and runs fine. The motor has new carb kit, fuel pump diagram,filter, rings , seals , basically it has been completely re built. It has standard.45 main jet. Do I dare put a smaller main in it?
Submitted: 2 years ago.
Category: Boat
Customer: replied 2 years ago.
Motor serial no starts with 143
Expert:  Tan replied 2 years ago.
Hello. My name is***** will be assisting you today. The engine is starving for air or you have an exhaust leak. The reason removing the cowling helps is you are giving the engine clean air. Check for an exhaust leak.
Expert:  Tan replied 2 years ago.
I would suspect the base gasket # ***** as the place for an exhaust leak.
Expert:  Tan replied 2 years ago.
The other place you want to look is in the cowling. Check that the air vent # ***** in the cowl is clear and not clogged with spider webs, dirt dobber nests or and kind of blockage of air flow.
Post back with questions.
Customer: replied 2 years ago.
I have just put new gasket in air screen in cowling is not plugged. As matter of fact I removed it to see if it helped. It did not.
Expert:  Tan replied 2 years ago.
Ok that leaves an exhaust leak. The carbon monoxide gases from the exhaust are suffocating the engine. The exhaust cover will usually leak water. The base gasket can leak exhaust gases and not leak water. Now are you running the engine in a test tank or in the water?