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Mercury outboard 25hp pops when deaccelerating

B

Boulding

New member
I have a 2003 mercury 25hp.. bought it over the summer so I have no maintenance history on it. It's been running great all yr. Noticed today that when I pull the throttle back right before it gets to neutral, it makes a small popping noise. Still runs strong and smooth in fwd and rev. Pulled the plugs and they are black.. could this be my issue? Maybe I fouled a plug? Gas isn't old and I'm sure the mixture is correct.
 
Can you narrow down "where" the pop is coming from?

What you call a pop someone else may call a sneeze or a cough.

If it is coming from the base of the motor you could have a bad power head base gasket.

Coming from around the carb, a bad carb gasket.

Exhaust - exhaust gasket (base) or exhaust cover gasket.

Could be an transfer cover gasket on the intake.

Could be an upper or lower crank seal.

Coming from the throat of the carb it could be reed issues.

Sorry can't really narrow it down because there is (literally) a dozen potential sources of a "pop", and that is assuming it's not a "mechanical pop sound" (something slipping somewhere).
 
galamb said:
Can you narrow down "where" the pop is coming from?

What you call a pop someone else may call a sneeze or a cough.

If it is coming from the base of the motor you could have a bad power head base gasket.

Coming from around the carb, a bad carb gasket.

Exhaust - exhaust gasket (base) or exhaust cover gasket.

Could be an transfer cover gasket on the intake.

Could be an upper or lower crank seal.

Coming from the throat of the carb it could be reed issues.

Sorry can't really narrow it down because there is (literally) a dozen potential sources of a "pop", and that is assuming it's not a "mechanical pop sound" (something slipping somewhere).
Click to expand...

It just started making the noise, my 1st boat motor but it sounds like some sort of backfire. I haven't gotten that close to it to distinguish what part of the motor it's coming from. What are some things I could do to see if it solves the issue before I take it to a shop? Seafoam? Change the spark plugs?
 
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