15 HP Merc 2-stroke rough idle

buzzkill · #1 (**permalink**) 10-12-2009, 04:10 PM

The motor is idling rough but works perfectly fine at full speed. "Coughs" at idle and during slow speeds (idle to around 1800 rpm is my guess). Sometimes coughs and shuts off. Same problem with hot and cold weather.

I've run 12 gallons of new fuel (87 octane) with proper oil/fuel mixture, small engine repair chemical and carb/injector cleaner. Plugs are ok. Problem still exists.

My next mission would be to take apart the carb for cleaning.

Thoughts?

boats.net · #2 (**permalink**) 10-12-2009, 04:24 PM

The cough is a sign of lean running which means low speed circuit in carb is plugged or restricted. Need to remove and clean carb.

buzzkill · #3 (**permalink**) 10-13-2009, 12:00 PM

Thanks!

Can I use parts/brake cleaner spray to clean the carb?

boats.net · #4 (**permalink**) 10-13-2009, 01:20 PM

It wont dissolve the varnish from old gas, you can use Mercury's Power Tune 858080K01 it works to soak parts in.

buzzkill · #5 (**permalink**) 10-13-2009, 01:33 PM

Ok. So I remove the carb and soak the entire unit in this solution...or should I disassemble the carb and soak individual parts?

boats.net · #6 (**permalink**) 10-13-2009, 04:12 PM

Disassemble and soak then blow out passages and jets with compressed air to clear any blockage.

buzzkill · #7 (**permalink**) 10-17-2009, 01:29 PM

I forgot to mention that when the motor 'coughs', it also puffs blue smoke...as well as running cold. Sometimes it will cough to a stall out, however only at low idle speed. During acceleration, blue smoke also is present. I took the carb apart and cleaned with basic cleaner, problem still exists.