2010 Mercury 4-stroke 3.5 HP stall on idle

[wahnamch]

We've run this engine for just a few hours each year since purchase. This is the problem we have had this season:
- Starts normally from cold (using choke)
- Pushing in choke when running, the engine runs just for a couple of minutes and then stalls if in idle
- Keeping high revs will keep the engine running for a few minutes more, but as soon as it is returned to idle, it stalls again
- I can't find any adjust on the mixture (seems to be fixed)
- Spark plug is black when removed. I changed it for a new one (correct gap set) and it came out black after just a short running time and had no influence on the stalling

Any thoughts would be much appreciated,

 

[wahnamch]

Nobody have any suggestions for this?

 

[wahnamch]

Just in case anyone else runs into this in future, I did manage to solve the problem with a little experimentation.

The problem was the choke flap wasn't opening properly. I guess it was a little stiff or something. I just dismantled the carb, sprayed a little WD40 on the choke flap joints (inside and outside of the carb), opened and closed the flap about 20 times to get the lubricant into the joints properly, let it dry, wiped of the residues, then closed it all up. Took out the spark plug, cleaned it and reset the gap before putting it back in.

Now it runs great. Starts first time, idles perfectly once nicely warmed up.

Hope this helps someone else, too.

Happy boating!