Testing Procedure; Starting Circuit; Charging Circuit - Tecumseh ECV100 - 120 Technician's Handbook

TESTING PROCEDURE

STARTING CIRCUIT

1. Check the power source using an electrical tester and follow the testers recommended procedure. Make sure the
battery meets the minimum battery voltage requirements found in the original equipment manufacturer's service
manual.
2. Check the electric starter terminal for the required voltage (12v D.C. or 120 v A.C.) using a voltmeter.
CAUTION: FOLLOW ALL SAFETY PRECAUTIONS WHEN TESTING FOR A.C. VOLTAGE, ELECTRIC SHOCK
CAN KILL.
3. Check wiring, connections, fuses, ignition or starter switch, safety switches, or solenoid for continuity using a
ohmmeter or a continuity light. Repair or replace as necessary.
4. Remove all equipment loads from the engine. Take off all drive belts, chains, and couplers to isolate the engine from
the equipment it is powering.
5. Try to turn the engine over using the recoil assembly if equipped. If the engine doesn't turn over, a mechanical binding
may be the cause. Check for proper lubrication (oil level and viscosity), starter gear and flywheel ring gear interference.
If no problem is discovered, the problem is an internal failure.
6. If the engine binds only on the compression stroke, check the engine valve clearance per the specification table in
Chapter 10. If the valve clearance is within the specifications, the camshaft (compression release) may require
replacement. Valve clearance not within the listed specifications will require either resetting or grinding the valve
stems to obtain the proper clearance.
7. If the engine turns over freely, the electric starter should be disassembled and checked. If the preceding steps fail to
correct the problem, the engine will require disassembly to find the mechanical failure. See Chapter 9 under
"Disassembly Procedure".

CHARGING CIRCUIT

The following pages will show wiring diagrams of several Tecumseh charging systems. The charging system used on the
engine is best identified by obtaining the engine model number and the specification number on the engine. Consult a
Tecumseh dealer or a parts manual to identify the charging system. To make many of the tests it is necessary to run the
engine and measure alternator output with a voltmeter. When making voltage tests with the engine running, it is not
necessary to take readings at all the listed R.P.M.s. Checking at one of the speeds is sufficient.
In some cases an open circuit D.C. check cannot be made. An SCR (Silicon Controlled Rectifier) is located in the circuit
which requires a minimum "turn on" voltage to allow it to conduct. Without the battery in the circuit this "turn on" voltage
is not present. The SCR "senses" this and there will be no D.C. output from the regulator or rectifier.
Each charging system has its own testing procedure. Test the charging system using the applicable procedure on the
following pages.
350 Milliamp Charging System
Models: Rotary Mower Engines Equipped
with Electric Start
CHECKING THE SYSTEM: The battery must be in the
circuit to perform the test properly. Connect a voltmeter
across the battery. The voltmeter should read the battery
voltage. Start the engine. With the engine running, there
should be an increase in the voltage reading. If there is no
change in the voltage reading, the alternator is defective
and should be replaced. See Chapter 9 for "Disassembly
Procedure" (diag. 11).
NOTE: SET THE VOLTMETER TO THE 0-20 VOLT D.C.
SCALE FOR THE TEST.
48
(-) ENGINE GROUND
MAGNETO GROUND
D.C. OUTPUT
(GR)
LEAD (RED)
ELEC. STARTER
LEAD (ORG)
BATTERY
GROUND (BL)
RED
BLACK
(+) POSITIVE LEAD
11