Briggs & Stratton Twin Cylinder L-Head Repair Manual page 19

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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 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
The cylinder balance test will also detect a cylinder that
is not functioning. When grounding out one cylinder
there will 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 varied 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 equip-
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ment 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 adjust-
ment.
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.
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 acceleration. Check for fit, or tightness.
2. No lubricant in transmission or gear box.