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Tan, MerCruiser Certified Technician
Category: Boat
Satisfied Customers: 10977
Experience:  40 yrs. experience with complete engine repairs both inboard/outboard and MerCruiser Certified Technician.
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My 4hp 4stroke mercury outboard stalls when on more

Customer Question

my 4hp 4stroke mercury outboard stalls when on more throttle. cleaned the carb, fuel flows when hose made loose. Putting on extra choke makes it run quite OK. Dnt have a clue!
JA: Sometimes boat issues seem like they'll be really complicated, but end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: motor is 10 years old, 6 years ago a new carb was fitted, 2 years ago new gas hoses. Carb seems the problem, but also seems quite clean.
JA: Is there anything else important you think the Marine Mechanic should know?
Customer: it runs idle and on slowest speed. When throttle isput a put on the start sign it runs, and sometimes stalls. When throttled up stalling is quite immediate. This can be managed using the choke. I woud think there is a gas issue. Or may be a plugging in an more unusual place....
Submitted: 12 months ago.
Category: Boat
Expert:  Tan replied 12 months ago.

Hello. My name is Tan.

The use of the choke helping is the clue. The choke creates a vacuum in the venturi allowing more fuel into the combustion chamber and making engine run better. This is due to the carb being clogged.

You have a clogged carburetor. These carbs are bad about clogging up and they must be cleaned in an ultrasonic tank. Conventional cleaning doesn't work. The ports are so small that hard fuel just cab be cleaned out with carb cleaners alone.

This is especially true on engine that sit allot.

Most marine repair facilities have ultrasonic cleaning tanks.

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