You could have a bad coil/magnetto. Or it just might need to be cleaned (sanded to get the rust off of it and the flywheel.
The most comon cause of an engine that keeps revving up and down (aka surging) is a dirty air filter.
If the wrong oil is used in a lawnmower, do not start it. Simply drain the oil as completely as possible and fill with the proper oil.
You have your lines on wrong. Make sure you have the one with the arrow in coming from the tank, the one pointing out goes to the carb and the one with no arrow goes to the last one
You may do serious damage to the lawnmower if the wrong spark plug is installed.
flywheel key could be sheared OR check valve settings as likely the cam followers are on the wrong valve.
remove spark plug, remove air cleaner and hold hand over top of carburettor and pull start cable a few times , then reassemble and restart, also check fuel quality, ie water contamination
it is losing its prime... i have the same problem right now and i have cleaned the carburetor, changed the gas and spark plug and changed the air filter. The only thing that i can think of is that there is something wrong with the priming bulb or the gas cap is hindering the air flow... still trying to repair....
What is wrong when your toenail starts turning green?
On Uranus I,m afraid you are wrong. The mechanical lawnmower was invented by an English engineer Edwin Budding from Stroud in 1830.
it starts without gas?