Onan MJA Series Service Manual page 43

41 3.3 Ignition
System
All models (MJA, MJB, MJC) are equipped with a 12 volt battery igni­
tion system. The,. function of this system is to provide a spark in each
cylinder at the correct time to ignite the fuel air mixture. All systems
use suppressed ignition components to minimize radio interference.
The 4 cylinder model (MJC) uses a battery ignition system with dual
breaker pOints
~d.}gnition
coils.
3.3.1 TESTING
The most complete test for an ignition system is to check the final re­
sult -- spark on the spark plugs. Remove each plug in turn, reinstall
the ignition wire to that plug and hold the plug base against a piece of
bare engine metal. Then crank the engine and watch
the
spark. A
good blue spark indicates a healthy ignition system, a weak or yellow
spark or no spark, a poor ignition system. The defect can be caused
by defective breaker points, coil, condenser, or wiring. A good spark
on all but 1 cylinder indicates a defective spark plug or defective high
tension wire.
3.3.2 :MIA IGNITION SYSTEM
This ignition system, Fig 3. 3. A, uses a conventional automotive 12
volt coil, battery ignition to fire the single spark plug. Except for the
coil, the system is similar to the ignition system for the 2 cylinder
MJB
models. For information on maintenance, timing, breaker points,
condenser, or
co~l
see
M.JB
IGNITION SYSTEM, Sect 3.3.3.
HIGH TEMPERATURE
CUT OFF SWITCH
,.---iE7....,
L ; . " . - ­
TO CONTROL
If
BOX TERMINAL
I'
d
BLOCK
II
II
II
II
II
II
\1
II
} \
t;;-"':-===~~
::;;. ::alll
I
I
IGNITiONI
II
COIL I II
I II
IGNITION
I
IIBREAKER POINTS
L ___
..J
I
I
I
I
r--'
6;11
II I -J:.I
\ I ~"-____
I ·
I
--::0
I
-=
1-=== I
FIG 3.3.A - MJA IGNITION SYSTEM
L~~
"
1"