Chapter 7 Ignition System; Ignition System Operation; Timing Adjustment - Tecumseh VLV Technician's Handbook

SOLID STATE IGNITION. Tecumseh's solid state
capacitor discharge ignition (CDI) is an all electronic
ignition system and is encapsulated in epoxy for
protection against dirt and moisture.
SOLID STATE IGNITION OPERATION. As the magnets
in the flywheel rotate past the charge coil, electrical
energy is produced in the module. This energy is
transferred to a capacitor where it is stored until it is
needed to fire the spark plug.
The magnet continues rotating past a trigger coil where
a low voltage signal is produced and closes an electronic
switch (SCR).
The energy which was stored in the capacitor is now
transferred through the switch (SCR) to a transformer
where the voltage is increased from 200 volts to 25,000
volts. This voltage is transferred by means of the high
tension lead to the spark plug, where it arcs across the
electrode of the spark plug and ignites the fuel-air
mixture.
SPARK PLUG SERVICE. Spark plugs should be
replaced periodically. Check electrode gap with wire
feeler gauge and adjust gap to .030". Replace if
electrode is pitted, burned or the porcelain is cracked.
Refer to Master Parts Manual for correct replacement
number. Use a spark plug tester to check for spark.
If spark plug fouls frequently, check for the following
conditions:
1. Incorrect spark plug
2. Poor grade gasoline
3. Breather plugged
4. Oil level too high
5. Engine using excessive oil
6. Clogged air cleaner
24
Chapter 7
IGNITION
Not For Resale
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The proper air gap setting between magnets and the
laminations on CDI systems is .0125''. Place .0125''
gauge, Part No. 670297 between the magnets and
laminations and tighten mounting screws to a torque of
30-40 inch pounds. Recheck gap setting to make certain
there is proper clearance between the magnets and
laminations. NOTE: Due to variations between pole
shoes, air gap may vary from .005/.020'' when flywheel
is rotated. There is no further timing adjustment on
external lamination systems.
IGNITION TIMING. The flywheel key is what times the
ignition for the engine. If this key is partially sheared
from striking an object with the blade. The timing and
engine performance could be affected. The key should
be inspected if a performance problem exists.