1996 Mercury Mariner 125hp rough idle

"Hi there I have a 1996 Mercur

"Hi there I have a 1996 Mercury Mariner 125hp I am told that it is a 2+2, did they make this kind of motor in 96 and has anyone experienced any problems with a rough motor idle at mid range. I am not sure if it is a carboration problem or something else. I changed the spark plugs and the fuel is good. The motor when running at low idle tends to sputter. Any help with this would be appreciated.
Thanks in advance."

If it is a 2+2 then the lo

If it is a 2+2 then the lower 2 carburetors do not operate the same as the upper 2 at idle.The idle jets are very small and only allow fuel in for cooling and lubrication.As speed is increased the 4 carbureters start operating on the high speed jets.There is a range where it will run rough. It is important to check compression and spark when trouble shooting.No point in guessing on a fine motor.

"Hi there. Thanks for respondi

"Hi there. Thanks for responding to my question. I am still not sure how to determine if this is a 2+2. Can anyone tell me exactly how to do this. We bought the boat used and the person we bought it from says that it is a 2+2, however I have no way of finding out without taking the carborators apart and seeing. Is there any markings that I should be looking for on the engine. I only ask as I want to be sure before getting into something. If the engine is a straight 125 then there should not be the rough idle, however if it is the 2+2 then I have my answer and can move forward. Thanks in advance."

Look carefully on the port sid

Look carefully on the port side of the carburetors. The upper two have an adjusting screw for low speed mixture and the lower two do not.