shu9265 Posted June 8, 2020 Share Posted June 8, 2020 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 ? Link to comment Share on other sites More sharing options...
jerryriggin Posted June 8, 2020 Share Posted June 8, 2020 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. Link to comment Share on other sites More sharing options...
shu9265 Posted June 9, 2020 Author Share Posted June 9, 2020 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. Link to comment Share on other sites More sharing options...
jerryriggin Posted June 9, 2020 Share Posted June 9, 2020 I would go back to a bag if it just started this year. Link to comment Share on other sites More sharing options...
Realmeal Posted June 16, 2020 Share Posted June 16, 2020 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. Sent from my iPhone using Great Lakes Fisherman Mobile App Link to comment Share on other sites More sharing options...
FBD Posted June 16, 2020 Share Posted June 16, 2020 Run a higher temperature thermostat? Link to comment Share on other sites More sharing options...
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