Just to put my two cents worth in here. The other expert is definately on the right track. Asking all these questions and getting the correct answers is the only way we are going to narrow down the possible causes of your problem.
Why did he ask these questions?
Is the mower being tipped or is it remaining level?
If a mower has been tipped, the air filter will fill up with oil and cause the engine to burn rich...causing the spark plug to carbon up like what you are talking about.
Does the oil in the crankcase smell like gas if you sniff it?
If the carburetor is overflowing because of dirt, gum, or varnish, it can fill the crankcase full of gas...thinning out the oil and causing the engine to burn oil very quickly and carbon up the plug. Also he asked this because if the crankcase is full of gas, that tells him that the carb must be rebuilt and it is giving too much gas to the engine also carboning up the plug.
What level is the oil at on the dipstick?
He wanted you to tell him this because this is a tel-tale sign that the crankcase is full of gas if the oil level is too full. If the oil level is low, then that tells him that the engine may be ruined because of lack of oil. The cylinder and piston may be scored and this would cause the engine to burn oil and to carbon up the plug.
How old is the engine?
This lets him know if the engine is old enough to be worn out. A worn engine will start to burn oil and carbon the plug.
What weight oil are you using?
Too many people don't know that if you use multi-grade oil (10W30 or 10W-40) Engines start burning oil very rapidly. You should always use a straight weight 30W oil in small engine like your's.
And what horsepower engine are we talking about?
This gives him the size of the engine so that he can picture other possible problems that may be unique to larger or smaller engines.
Is it overhead valve?
This lets him know if he should start giving you information about overhead valves. They tend to get out of adjustment much more than L-Head valve engines and also oil is more likely to find its way through the valve train into the combustion chamber. Causing your problem.
It is NOT...JUST A LAWN MOWER as you stated. It is a very finely tuned piece of machinery that can have many different causes of your problem.
Give this expert a chance to help you.
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