B&S burning oil

Joined
Dec 26, 2007
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My family owns a 1997 Lawnboy mower with a commercial grade 6hp B&S engine on it. I'll admit that the oil was not changed every season, and sometimes in its younger days it may have gone 3 years with no oil changes (I was younger at the time and didn't know any better). However, we typically mow 15hrs a season so that's not too bad. Anyway, I've been personally changing the oil consistently for the past few years now every season. Last year I did a Frankenstein mix of Mobil Clean/Pennzoil/Castrol 10w40. It would smoke a little bit on start up so I switched to HD 30. I put Castrol HD 30W in it this time, and it still smokes a little on start up for about 5 seconds...it blows black smoke out of the exhaust. Is this something to be concerned about, or could it possibly be the residual multigrade 10w40 in there getting burned out? Thanks.
 
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Jan 10, 2008
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Milwaukee, WI
Do you prime or choke it? Black smoke is more likely rich combustion than oil burning. But anyway, it's not something to be concerned about.
 

GMFan

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The air filter is cleaned and re-oiled every year with the oil change. Plug was changed a year ago (I do the plug every other year).
 
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Apr 22, 2007
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Houston, Tx, USA
A carb cleaning and tune wouldn't hurt, but then neither does the smoke, so I wouldn't sweat it unless you get bored and want to take apart a lawnmower's carb. Also, this could be leaking valves, in which case you really don't want to deal with it and it doesn't matter anyway.
 
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Alabama
I'd try a double dose of Seafoam in the gas before I did anything else. Like bepperb said, black smoke is a sign of a rich condition. Before I got my ZTR, I had a lawn tractor with a 15hp Kohler that was running bad, belching a little dark smoke. A tank dosed with Seafoam (I used twice the recommended amount) soon returned it to the smooth running motor to which I was accustomed. BTW, I gave that mower to my brother three years ago and it's still running like a champ.
 
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ON, Canada eh?
If it's running too rich this could be why it's burning oil as it's washing the cylinder walls... I would take the Carb apart, thoroughly clean it and replace any worn parts/seals etc. and reassemble. Then setup the fuel mixture if it's an older style and you should be good to go! If it still burns oil, then switch to a heavier weight...
 
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