3-40 ENGINE • Clean and assemble the head and valve components. Fill the intake and exhaust ports with gasoline to check for leaks. • If any leaks occur, inspect the valve seat and face for burrs or other things that could prevent the valve from sealing.  Always use extreme caution when handling gasoline. VALVE SPRING The force of the coil spring keeps the valve seat tight. Weak- ened spring results in reduced engine power output, and often accounts for the chattering noise coming from the valve mecha- nism. • Check the valve spring for proper strength by measuring its free length and also by the force required to compress it. • If the spring length is less than the service limit, or if the force required to compress the spring does not fall within the range specified, replace the spring. Valve spring free length: E Service limit: (IN. & EX.) : 37.5 mm (1.48 in) L 147 N 09900-20102: Vernier calipers Valve spring tension (IN. & EX.): P 33.55 mm Standard: M Approx. 147 N, 15.0 kgf/33.55 mm (33.1 lbs/1.32 in) SA