Try compression test on 3 and 4, (wet test procedure) pour a small amount (enough to cover the cylinder wall) of oil into the cylinder through the spark plug hole.
- if adding the oil increases the compression, the piston rings and/or your cylinder bore may be worn or damaged.
- if the pressure stays low, a valve may be sticking or seating improperly, or there may be a leakage past the gasket, valve oil seal.