Engine loads up with carbon while trolling

[shu9265]

I have a merc cruiser 165 3.7 I/O

Thing runs like champ. Goes fast goes slow.  Problem is, when I slow to troll speed 1.5-2.0

My engine loads up with carbon. When I rev the engine up, it blows black junk on the water. It will do that for a few minutes and then clear itself.

Are my plugs too cold?

Or is this a carb issue ?

 

 

 

[jerryriggin]

Are you running trolling bags? It would help a bunch to get the rpms up while trolling. If putting a load on the engine with bags doesnt clear it up I'd lean towards carburetor.

[shu9265]

I have been running (1) bag, but I switched over to a Happy Troller plate this year

 

I will ask my local merc guy to have a look at carb settings.

[jerryriggin]

I would go back to a bag if it just started this year.

[Realmeal]

I had this happen years ago and my mechanic put some hotter plugs in and it helped. I always ran bags and I could never totally solve the issue.


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[FBD]

Run a higher temperature thermostat?

[CJ428]

I had a new 8HP Merc I used for trolling. It would load up and misfire every 15 secs. I had to change the jet in the carb. I cannot remember If I went smaller or larger .  If you order them get one smaller and one larger.  There may be a mixture screw on your carb-try that.