1998 40hp Mariner/Merc coughs

[wingsaircharter]

I have a 1998 3 cylinder Mariner/Merc that coughs at idle and just above. It is on a pontoon boat so that is the speed that it usually runs at. Put in new plugs and drained the carbs looking for moisture but that is about it. It runs fine at 1/2 throttle and above. Any ideas or info from someone that has fixed the same problem would be great. Thanks!

 

[joed]

Re: 1998 40hp Mariner/Merc coughs

Had a similar problem on a 95 9.9hp. Problem was exhaust port plugged with carbon deposits. Powerhead had to be removed and the port chipped out. 1 hour labour in the shop.