I had a neighbor who "refilled his riding mower crankcase". He got rid of the mosquitoes before realizing he forgot to drain the old oil out. Then there was the time when my mower smoked terribly. I shut it down and discovered a stuck open float valve and the crankcase was overfilled with gasoline.
Too much oil. Check the air filter and see if it has oil on it. My Honda's oil level is measured with the dipstick NOT screwed in. Check your manual. Hope this helps.