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I was having problems getting mower to start. Got another battery and replaced the plug which was all black. It started and blew out a lot of white smoke and oil is spewing from the exhaust. One of the exhaust manifold bolts was broken and oil was coming out there also. I checked the oil level and the oil appears to be very thin and smells like gas. Tractor has definitely not been tipped over. Is this a blown head gasket or another issue?

White smoke can be the result of a serious issue like a blown head gasket, a damaged cylinder head, or a cracked engine block

Gas in the oil from bad valve in carb, Drail oil put new oil and run it out of gas until you fix the carb.

I have a new mower and it is blowing white smoke the first time I used it??

Fuel is leaking from carb into open valve on engine, turn off fuel supply until it doesn’t leak and it may be a bad solenoid on bottom of carb bowl, change oil and only turn on gas when using until you fix the valve and there is a main seat in carb for the float that could be leaking into the motor from gravity feeding from the tank and if the motor fills up with fuel remove spark plug and blow fuel out and change the oil and filter etc and the motor could hydro lock and damage the motor permanently. Basically fuel is not being controlled and running through an engine valve and if it is water cooled you may have blown a head gasket that would be the white smoke. Take the mower back!