Have you removed the muffler cover every year and cleaned the muffler and exhaust ports?

Also it probably needs crankshaft seals and/or the reed valve may be worn out. There are a lot more possibilities than just low compression. I think compression should be 90 PSI minimum, but others may have the exact specification.

Thank you for your response.
What is the best method for cleaning the mufler and the exhausts ports?
Thank you.
Jean

You have to remove the blade and blade driver to access the muffler cover. Removing the muffler cover should reveal the exhaust opening from the engine. Looking in that opening you will see the three exhaust holes. They are probably blocked with carbon to some extent. Rotate the engine until the piston covers the holes, then use a piece of wood dowel rod to clear them. Try to vacuum out the carbon pieces as well as you can before starting it. The muffler may have to be soaked in solvent to get the carbon out. If the mower is self-propelled, the drive pulley on the crankshaft may complicate muffler plate removal. The pulley is supposed to be removable but most of them are really stuck.

When you spin the flywheel by hand, IF it hits compression and rebounds, it has enough compression to run, not very technical but practical.

Walt Conner

Hello all,
My lawn boy is now running well, except the air vane i can't adjust very well, it speeds up and slows down continually.
But even so, i have clean the carburetor and the exhausts ports.
Do you know how to adjust correctly this air vane?
Thank you,
jean.
It is a 8440 model from 1988, serial: G 316 C 0378