Generac Power Systems GTH760 Service Manual page 12

SECTION 1: GENERAL INFORMATION
INLET GUAGE
PRESSURE SET
COMPRESSED
POINT
AIR IN
AIR PRESSURE
REGULATOR
0
0
REGULATOR
ADJUSTMENT
KNOB
RED RANGE INDICATES
UNACCEPTABLE LEAKAGE
OUTLET
GREEN RANGE INDICATES
0
GUAGE
ACCEPTABLE LEAKAGE
Figure 1-12. Cylinder Leakdown Tester
RESULTS:
1. 0-10% Cylinder is good
2. 10-30% there may be a problem
3. 30-100% Cylinder requires repair
THINGS WHICH AFFECT BOTH CYLINDERS:
1. Carburetion
2. Crankcase vacuum
3. Ignition timing
a. A partially sheared flywheel key will effect ignition timing and
engine performance.
THINGS WHICH AFFECT ONE CYLINDER:
1. Spark plug
a. A fouled spark plug may indicate the carburetor is out of
adjustment.
2. Leak in spark plug wire
3. Head gasket
4. Intake manifold
a. A leak at either end of the intake manifold will only affect one
cylinder, not both.
5. Valves
6. Rings
7. Piston
8. Cylinder
OUTLET GUAGE
PRESSURE
NOTE: A twin cylinder engine will run well on one cylinder as long
as the power required for the application does not exceed the power
produced by the one cylinder.
EQUIPMENT AFFECTING ENGINE OPERATION
Frequently, what appears to be a problem with engine operation, such
as hard starting, vibration, etc., may be the fault of the equipment
rather than the engine itself. Listed are the most common effects of
equipment problems, and what to look for as the most common cause.
HARD STARTING OR WILL NOT START:
1. Loose belt - a loose belt like a loose blade can cause a backlash
effect, which will counteract engine cranking effort.
2. Starting under load - see if the unit is disengaged when engine is
started; or if engaged, should not have a heavy starting load.
3. Check remote control assembly for proper adjustment.
4. Check interlock system for shorted wires, loose or corroded
connections, or defective modules or switches.
ENGINE WON'T STOP:
1. Check equipment ignition stop switch.
2. Check for loose or disconnected equipment stop switch wire.
3. Check ground wire harness on engine.
a. See Section 2 for test procedure.
VIBRATION:
1. Unit load out of balance (pulley, clutch or blades) - remove and
replace.
2. Mounting bolts loose - tighten.
POWER LOSS:
1. Bind or drag in unit- if possible, disengage engine and operate
unit manually to feel for any binding action.
2. Unit load has excess drag.
NOISE:
1. Engine coupling or pulley - an oversize or worn coupling can result
in knocking, usually under acceleration. Check for fit or tightness.
2. Equipment needs lubrication.
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