I have a Craftsman lawn mower that would not crank over so I thought I It was the starter unit so I bought a new one and I Installed It and It still would not start so I took the spark plug out and It turned over...But now It smokes like hell.:-(
This sounds like you had a hydraulic lock caused by fuel leaking into the cylinder.
When you tried to crank it over the fuel pressurises and does damage to the engine.
In most cases it blows the head gasket.
Next most common is breaking a ring
Last, if you are really unlucky it can crack the head.
The other thing that happens is the fuel leaks down past the rings and fills up the crankcases.
This dilutes the oil and reduces the volume of air in the crankcase so when the engine starts up you get massive amouts of oily fuel blowing into the carb via the breather and lots of oil in the combustion chamber will make you engine smoke like hell.
So for startere check the oil.
If it is too high, to thin and/or smells a bit fuely change the oil , run the engine for 10 minute or so then change the oil again.
If the motor runs properly then you are lucky & 1/2 way home.
You now have to address the leaking fuel problem by cleaning the float valve in the carb.
OTOH if the engine does not run clean after the two oil changers and a reasonable amout of running time.
As the queen of spades said to Alice " off with your head "
