I am sorry to hear about your problems, hopefully I can help you. Additionally, your English
is much better than any foreign language I speak!
To begin with, low oil pressure usually does not cause overheating
. Low oil can, because oil also carries away heat but oil pressure by itself does not.
How do you know it overheats, does it start smoking or sizzling?
Will it run at full power before it overheats and then the power starts decreasing?
If it has not been done yet, the thermostat needs to be removed and tested. It is located on the top of the engine between the drive belt pulleys. Remove it and put it in a pot with water
and put on the stove and have a thermometer. Look at the thermostat, it is closed but should open up when the water
reaches 60C. If it does not, replace it.
The water pump impeller also needs to be inspected, you will need to pull the "lower unit" off to do that. It is simple but much easier if you have someone show you the first time. If the impeller is worn or broken, replace it. clean the passages out with wire or blow them out with compressed air.
Reassemble those parts
and then adjust the carburetor, as running with too little fuel (called "lean") can make it run hot too. First adjust the idle by connecting a tachometer and adjusting to 950 RPM
, +/- 50 RPM, then adjust the linkage.
I hope that is a help!