Poor performance, or does air leak out of the intake air filter while the unit is running? This is probably the problem. Damaged/sticking valves is a common issue when you have low compression, and can also cause the motor/engine to stall and too much pressure in the pump’s crankcase. Be sure to clean the head and cylinder very well so as to remove all of the old gasket material and build-up (carbon and rust) when re-installing.
15-pc Thunderbolt Black Oxide Drill Bit Set
1/4" x 50 Ft Noodle Air Hose with Coupler and Plug