1998 40hp tuning questions

[Jaxbeach]

i have a 1998 40hp mercury tracker 3cyl. 2 stroke that "coughs" when at idle. Motor runs fine oyher wise. I have changed plugs, removed and cleaned carbs. Any sugestions on what might cause this stumble?

 

[racerone]

One of the carburetors may be running lean.----Try opening low speed mixture adjustment to see if cough goes away.-----------All throttle plates must be closed at idle.

 

[Jaxbeach]

Thanks I'll try it. I took it out and ran it yesterday ran great at WOT but started coughing under 2K RPM. The indle screws are open aprox. 1 1/4 turns . Does that sound about right?

 

[racerone]

What they are right now does not matter.-----Try opening them a bit more if it is indeed a " lean cough "!