mercury 40 hp 4 stroke carb

[MATEY]

Ihave a 2001 40 hp 3 cylinder 4 stroke. Engine starts perfect, idles and slow speed perfect, full speed perfect. However when trottling from slow speed to full speed engine seems to get to much fuel and chokes. Have to give several quick twists to trottle in oredr to pick up speed. also if reducing speed too quickly engine stops. engine also runs erratically at mid range speed.

Any sugestions.
thanks
matey

 

[achris]

Re: mercury 40 hp 4 stroke carb

Sounds like you need to pull the carb, strip and clean it..

Have you tried new spark plugs?

Chris.........

 

[mthieme]

Re: mercury 40 hp 4 stroke carb

I worked on a 2004 Mariner 40hp 4 cyl this summer with a carb problem...had three carbs.
The seat for the needle was nothing more than a thin copper washer. In the uppermost carb, the needle never seated properly causing the upper carb to drip fuel.
I assume it uses the same carb. Someone will correct me if I'm wrong.
Anywho, I didn't think much of this design.

 

[MATEY]

Re: mercury 40 hp 4 stroke carb

plugs are new. I read somewhere that there is no adjustment for the 3 carbs.
Does anyone know if this is true. Also was wondering about three screws on small lever attached to each carb. They look like adjustment screws.

matey

 

[mthieme]

Re: mercury 40 hp 4 stroke carb

That sounds like the idle adjustment.
Is this the only screw you can find?
Look for a screw in front toward the bottom.
This would be your mixture adjustment.

 

[hamit59]

Re: mercury 40 hp 4 stroke carb

your right about the carbs that design is not the best I have ever seen.
It makes me wonder about these new engineers. after 3 tries I just had to replace the carb. I couldn't get the new seat to seal off with the needle valve.