Equipment Affecting Engine Operation - Briggs & Stratton 405777 Series Manual

SPARK PLUG LEAD
Fig. 9 − Cylinder Balance Test
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.
If the RPM loss is greater than 75 RPM this indicates that
the cylinder with the least RPM loss is the weakest of the
two cylinders. Look to that cylinder for a problem. See
Example.
Example:
Engine RPM − Both Cylinders = 3400 RPM
Engine RPM − #1 Cylinder Grounded = 3300 RPM
Engine RPM − #2 Cylinder Grounded = 3100 RPM
Conclusion: #1 cylinder is weakest of the two cylinders.
Things Which Affect One Cylinder
1. Spark plug
a. A fouled spark plug may indicate that 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
The cylinder balance test will also detect a cylinder that is
not functioning. When grounding out one cylinder there will
SPARK PLUG
GROUND
WITH
SCREW DRIVER
TSM
be no RPM loss. When the other cylinder is grounded out
the engine will stop.
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 powered rather than the engine
itself. Since many types of equipment are powered by
Briggs & Stratton engines, it is not possible to list all of the
various conditions that may exist. 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 cor-
roded 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.
a. See Section 3 for test procedure.
Vibration
1. Cutter blade bent or out of balance − remove and balance.
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. Grass cuttings build-up under deck.
3. No lubrication in transmission or gear box.
4. Excessive drive belt tension may cause seizure.
Noise
1. Cutter blade coupling or pulley − an oversize or worn
coupling can result in knocking, usually under accel-
eration. Check for fit, or tightness.
2. No lubricant in transmission or gear box.
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