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4.3l Mercruiser with black/grey smoke--need help troubleshooting

E

Eric A

New member
Today I took the boat out for a last run for the season. it's been several weeks since I've had it out but it ran great the last time out. Last night we had a cold snap so I put a heater under the boat cover (19ft bowrider). The outside temp was only 2 degrees below freezing for only 2 hrs so I thought the heater would be fine.

Anyway, I had it on the boat ramp and tried to start before unhooking the boat as usual. It was very difficult to crank so I gave it some extra fuel. It finally cranked over but ran rough with lots of smoke. I also noticed a sheen on the water that looked oily. When I returned to idle it stalled. After about 5 minutes of this I decided not to chance a trip out and came home to winterize the boat. The water that I drained out was very dark with an oily sheen on the surface.

What can I do to begin to troubleshoot this problem? Will I cause further damage to try to run it in the driveway with the muffs on? Thank you for your help and suggestions.
 
Thank you all for your responses. As it turns out, the oil was clean and, although it was not the choke, the problem was related to air intake. The spark arrester was SERIOUSLY dirty and clogged. And thanks to a post on another forum I was able to clean it very quickly with carb cleaner and forced air and finish up with brake cleaner so it dries quickly. This is my first year having it and it seems like it was not cleaned in years. Engine runs great now that it can breathe!
 
Actually that is the same as a choke issue......lack of air makes it run very rich just like a closed choke.

A simple wipe down with a good rag is all that is needed.........
 
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