Before adjusting the jet screws to fix something caused by other factors, look for a clogged fuel filter, air cleaner, or muffler. Check the condition of the fuel lines and the fasteners on the carburetor. Make sure the primer button is soft and not cracked. These saws use a Walbro brand carburetor and an excellent article on troubles and repair can be found at: http://www.drystacked.com The pictures are out of focus and he neglects the pumper chamber action, but the theory is very helpful--especially the position of the lower chamber gasket/diaphragm. Hope this helps!