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Small Engines (Lawn Mowers, etc.)/blowing white smoke Briggs Stratton


QUESTION: Model 31C707-0154-E1 my 17.5 hp just started blowing white smoke lots of it. The engine was getting harder to turn over when starting and when it started there was black and white smoke for a few seconds.

ANSWER: Does the oil smell like gas and is the oil thin and runny?

When was the last time the oil was changed?

What weight oil are you using?


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QUESTION: Eric, thanks for the quick answer and yes the oil does have a gas smell and appears to be runny, the oil was changed last fall before I put it up for the winter.

It is possible, and likely, gasoline leaked into the engine oil through the carburetor over the winter.  This is common as the inside parts of the carburetor can leak when they get old.

I would go ahead and change the oil.  Refill with new SAE-30 oil.

I would also remove the spark plug and spray some carburetor cleaner in the cylinder.  Leave the spark out and turn the engine to spin it to get help clean oil out of the cylinder.

How old is the engine?

Do you have an inline fuel shut-off valve in the fuel line?


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Eric A. Jones


Lawnmower Repair . Certified Master Service Technician from B&S. Have 23 years experience on B&S, Lawn Chief, Weed Eater, Echo, Peerless, Wheel Horse, Snapper, Atlas, MTD, McCulloch, Homelite and many other numerous brands. Specialize in electrical repair.


Born and raised in the midwest. Started tinkering with engines when I was about 14 on my Suzuki RM-80. I began lawn mower repair at a small hardware store. I knew absolutely nothing. I read lots of repair manuals and met an older fellow who taught me many lessons. I continued working on small engines through high school and paid my way through college working on mowers at the same hardware store. Decided to get away from the midwest and mower repair so I joined the Air Force. I repaired air traffic control electronic equipment and ended up in Hawaii where I got a part time job at Small Engine Clinic. I gained a lot of experience from the Small Engine Clinic and had a blast repairing small engines. I then took the Briggs and Stratton Master Service Technician test and earned my MST. I then traveled to Wisconsin where I attended the factory update training seminar and received formal training. Continued working on mowers part time as I completed 20 years of military. Retired from the military on a Friday and continued in the lawn and garden industry the next Monday.

MAS Aerospace Operations BA Mathematics AAS Electronic Communications AAS Electronic Technology

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