Check Ignition (With Electric Starter); Check Ignition (Engine Running); Carburetion - Briggs & Stratton 405777 Series Manual

If the engine will not start and the cause of malfunction is
not readily apparent, perform a systematic check in the
following order:
1. Ignition

2. Carburetion

3. Compression
This check-up, performed in a systematic manner, can
usually be done in a matter of minutes. It is the quickest and
surest method of determining the cause of failure. The
basic check-up procedure is the same for all engine
models, while any variation, by model, will be shown under
the subject heading.

Check Ignition (With Electric Starter)

NOTE: Magnetron® ignition system requires a minimum of
350 RPM to produce spark.
With spark plugs installed, attach a #19368 ignition tester to
each spark plug lead and ground the other end of the tester
as shown in Fig. 5. Spin the flywheel rapidly with engine
starter. If spark jumps the tester gaps, you may assume the
ignition system is functioning satisfactorily.
WARNING: ON MAGNETRON® EQUIPPED EN-
GINES, spark will still occur with a sheared
flywheel key. A severe shock or kickback hazard
may exist.
NOTE: Engines equipped with Magnetron® ignition sys-
tem will still display spark at tester with a partially or fully
sheared flywheel key. A partially sheared flywheel key will
affect ignition timing and engine performance.
SPARK PLUG LEAD
Fig. 5 − Checking for Spark
If spark does not occur look for −
Improperly operating interlock system
Shorted equipment stop switch wire
Two closed diodes in ground wire harness
Incorrect armature air gap
Armature failure
TSM
SPARK PLUG
Check Ignition
(Engine Running)
If engine runs but misses during operation, a quick check to
determine if ignition is or is not at fault can be made by
installing Tool #19368 tester between the spark plug lead and
each spark plug, Fig. 6. A spark miss will be readily apparent
when the engine is running. If spark is good but engine
misses, check for a fouled spark plug.
SPARK PLUG LEAD
#19368
TESTER
Fig. 6 − Running Check
Check Ignition
(Fouled Plug or Other Causes)
To check for a fouled spark plug or a non-functioning
cylinder, attach Tool #19368 tester between the spark plug
lead and each spark plug. Start and run engine at top no
load speed. Now ground one spark plug, Fig. 7. The engine
should continue to run on the other cylinder. Repeat this
test with the other cylinder. If the engine will not continue to
run when making this test, the cylinder that is NOT
grounded is not functioning and/or the spark plug is fouled.
Install a new spark plug before proceeding. If miss
continues, problem may be carburetion or compression.
See Check Carburetion, Check Compression. Also see
Cylinder Balance Test.
SPARK PLUG LEAD
Fig. 7 − Checking For Fouled Plugs
SPARK PLUG
SPARK PLUG
GROUND
WITH
SCREW DRIVER
7