ENGINE - GAS (LIQUID-COOLED) TESTS AND ADJUSTMENTS Note: For high altitude operation above 4000 feet, use high altitude carburetor kit, to prevent over rich fuel mixture and black exhaust smoke.
Compression Test Reason: To determine the condition of pistons, rings, cylinder walls and valves.
6. Crank hot engine until highest compression reading is obtained. 7. Record pressure readings for each cylinder.
Test Equipment: •
Important: Avoid Damage! DO NOT overheat starting motor during test. Starter duty is 5 seconds one, 10 seconds off. Additionally, if throttle lever is left in slow idle position (air flow into carburetor restricted), compression could read up to 483 kPa (70 psi) below specification.
Specifications:
JDM59 Compression Gauge
Minimum Compression . . . . . . . . . . . . . 620 kPa (90 psi)
Procedure: 1. Adjust valve clearance to 0.15 mm (0.006 in.) with engine at top dead center (TDC) compression stroke. Engine must be “cold” (shop temperature, about 60 - 85°F (16 - 30°C). See “Valve Clearance Adjustment” on page 43 for procedure. Note: Be sure the battery is fully charged before performing procedure. 2. Run engine until it reaches operating temperature (thermostat opens, and both radiator hoses hot).
Results: • If pressure readings are above specification, adjust valves and check fuel and intake air systems. Check exhaust for restriction. • If pressure readings are below specification, squirt clean engine oil into cylinders and repeat test. • If pressure increases significantly, check piston rings and cylinder walls for wear or damage. • If pressure does NOT increase after retest, check for leaking valves, valve seats or cylinder head gaskets. • Install spark plugs and reconnect ignition coils when finished with testing procedure.
Valve Clearance Adjustment A
Reason: Check and adjust valve clearance for proper engine operation.
B
MX14235
3. Stop the engine, remove both spark plugs, and ground leads to block or use a spark tester (B). 4. Attach the compression gauge assembly (A) firmly into one plug hole. 5. Put throttle lever in fast idle (wide open) position. On FD671D engines, choke must be properly adjusted and fully open. Air filter must be clean.
Important: Avoid Damage! Perform valve clearance measurement or adjustment when the engine is at room temperature, 16 - 27°C (60 - 80°F). Proper valve clearance is essential for the engine to operate properly. Check valve clearance for each cylinder separately. Procedure: 1. Remove spark plugs. 2. Remove valve covers. 3. Turn the crankshaft clockwise until piston, visible in the spark plug hole, is at TDC (top dead center) of the compression stroke.
Engine - Gas (Liquid-Cooled) Tests and Adjustments - 43