rough idling outboard

[siwash]

So I ended up buying a 16' with an 18HP mid-80s Merc.  A few of you may recall that I was asking questions about boat buying as I shopped for one for a few weeks.  Boat's okay... price was so so... we will see when I get it out there. Seller started it after multiple tries. Seemed to work after it warmed up.  

 

At home, started after about 5 pulls or so.. not bad.  In forward acceleration, the engine seems to perform well. In reverse as well... But, in neutral it idles poorly and dies after e few moments. It seems to shake and vibrate then almost backfires (if that's a thing with outboards?) I should try to post a video (if possible?).  Is this a carb issue?  BTW, I changed out the gas and bought Shell Premium and added Seafoam. Maybe if I leave it overnight, the seafoam will break down some of the guck? Should I change out the plug and clean the carb?             Thoughts?

Edited June 26, 2022 by siwash

[siwash]

BTW, seller has not cleaned the carb.  

[pics]

Seafoam will only do so much.  The carb will probably have to be removed and cleaned.. one tiny piece of gunk will cause a poor running condition 

[siwash]

okay, thanks... and what about spark plugs? 

[Fisherman]

2 stroke, yes change the plugs.

[AKRISONER]

New plugs, pull the carb and clean it right out with carb cleaner. 
 

good luck