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Ignition
21
Troubleshooting the Ignition System
The purpose of the ignition system is to provide a spark in the combustion chamber at the proper time to ignite
the fuel/air mixture.
To troubleshoot the ignition system:
1. Examine the spark plug by following the steps
described in the spark plug section of this chapter.
2. After examining the spark plug, reinstall it, or a new
one to ensure a good spark plug is being used.
3. Disconnect the spark plug wire.
4. Connect a spark tester to the spark plug wire.
5. Connect the other end of the spark tester to the
engine block. See Figure 4.1.
NOTE: It only takes 1,000 volts to jump a 0.025” air gap in open atmosphere, it takes 10,000 volts to jump the
same gap at 120 psi, therefore an open air spark test in not valid.
NOTE: The spark should be a minimum of 10 Kv (10,000 volts) at pull over speed.
6. Make sure the engine stop switch is in the “RUN” position.
NOTE: Most stop switches used on MTD handheld products are spring loaded to the “RUN” position when it is
released. This prevents no-start situations caused by the customer failing to turn the switch on.
NOTE: Once the engine stop switch is moved to the “OFF” position, it sends a ground signal to the module.
The circuitry in the ignition module will latch the primary winding to ground until the engine stops. This
prevents the need to hold the switch in the “OFF” position until the engine comes to a complete stop.
7. Rapidly rotate the engine while watching the spark tester for sparks.
8. If no sparks are seen in the spark tester, test the module.
Figure 4.1
Spark tester
Never remove the spark plug and hold it against the engine block to test for spark. The fuel/
air mix coming out of the spark plug hole will catch on fire.
! CAUTION! CAUTION
CHAPTER 4: IGNITION