1984 OMC Sterndrive 2.5 L black substance (carbon?) in exhaust

[rmlewaz]

Hello everyone. Problem: I have a 1984 OMC Sterndrive 2.5 Litre Rochester 2 bbl. Last time I had the boat in the water, it started blowing white then blackish smoke (not heavy) and I noticed what I thought was an oil slick on the water. Running out of the water, it has what I assume to be carbon in the exhaust and a particular odor. All 4 plugs were heavily carboned up. Changed the plugs, added Seafoam. Runs good, does not run hot, oil pressure is OK...but still blowing out carbon. Unburned fuel? My question...a mechanic thinks the carb needs rebuilding (and it likely does in any case.) What else, if anything, could cause this? Would appreciate some help. Thanks.

 

[redneck joe]

Re: 1984 OMC Sterndrive 2.5 L black substance (carbon?) in exhaust

are your plugs gapped correctly? Need correct spark.

Also - I am a huge seafoam fan but I double the 'recipe' on the can.

 

[Bondo]

Re: 1984 OMC Sterndrive 2.5 L black substance (carbon?) in exhaust

Hello everyone. Problem: I have a 1984 OMC Sterndrive 2.5 Litre Rochester 2 bbl. Last time I had the boat in the water, it started blowing white then blackish smoke (not heavy) and I noticed what I thought was an oil slick on the water. Running out of the water, it has what I assume to be carbon in the exhaust and a particular odor. All 4 plugs were heavily carboned up. Changed the plugs, added Seafoam. Runs good, does not run hot, oil pressure is OK...but still blowing out carbon. Unburned fuel? My question...a mechanic thinks the carb needs rebuilding (and it likely does in any case.) What else, if anything, could cause this? Would appreciate some help. Thanks.

Ayuh,.... Welcome Aboard,.... Yer gettin' raw fuel in the exhaust, so rebuildin' or replacin' the Carb is the 1st place to look,...

 

[Howard Sterndrive]

Re: 1984 OMC Sterndrive 2.5 L black substance (carbon?) in exhaust

is the choke opening fully when warm? The heat pipe likes to rust out of the manifold on those. I have JB welded a couple back in.
Or rust in the manifold might be insulating the pipe from getting the heat to the choke.

 

[bruceb58]

Re: 1984 OMC Sterndrive 2.5 L black substance (carbon?) in exhaust

Ayuh,.... Welcome Aboard,.... Yer gettin' raw fuel in the exhaust, so rebuildin' or replacin' the Carb is the 1st place to look,...

I agree. Carb is too rich.

Adding snake oil is a waste of time.

 

[rmlewaz]

Re: 1984 OMC Sterndrive 2.5 L black substance (carbon?) in exhaust

Thanks for the responses. I appreciate your help. I am going to rebuild the carb. It does seem like the most likely culprit. Thanks to all.