black smoke on startup

[Lively1]

My 1999 Bayliner has a Mercruiser 3.0 and everytime I start it, it produces black smoke out the exhaust. I let it fast idle for maybe 45-60 seconds, and then it smooths out and the smoking stops. Once its warmed up the engine runs fine. Been this way since I bought it in the spring.

 

Is there something here to be concerned with? Any particular maintainence or adjustments to check? 

 

Thanks.

[Steve.e]

Had a searay that did the same when trolling for too long and then gunning it. Carbon build up most likely. I would rebuild carb and have it adj by a reliable mechanic.

[Gill-T]

Find some non-ethanol fuel stations.  Use SeaFoam gas treatment to help get rid of the carbon build-up.  Hopefully, there is nothing internal wrong with engine. 

[Great Lakes Lure Maker]

I had a mercruiser engine years ago that had carbon build up at trolling speed.  It was much older than yours, but valve lash adjustment corrected the problem. When you say "smooth out", is it idling rough? Before the valve adjustment, mine did the same thing. Something to think about if the other suggestions don't work. 

[Lively1]

Yes it does idle rough initially, while coughing the black smoke.  But not after warming up. I would say, a little rough, but not chugging like it would if a cylinder were mis-firing or timing was off.

 

I buy my gas at Olney's, I've been told me it's ethanol-free 91 octane gas.

[Rich D]

Sounds like poss choke issue, causing running Rich until warmed up. Poss carb rebuild or choke being gummed up. Good Luck

Capt Rich

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[Great Lakes Lure Maker]

Carb is definitely a possibility. Fuel filters as well. I would make sure your gas is fresh. Change the filter and clean the carb filter. Change plugs, check the operation of the choke,and if the problem still continues, have the valves checked. How many hrs on the motor?

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[lakebound88]

Rich D is spot on. Also, if you have a slight needle seat issue, you have dripping of fuel into manifold. Upon start up the sudden rush of intake is causing excessive fuel and a very rich start up causing the black smoke you speak of. Once running the dripping fuel is atomized by the constant intake. Good luck

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