Onan MJA Series Service Manual page 55

53 IGNITION SYSTEM
5. Connect primary leads to distributor terminals.
6.
Time ignition system. See Sect 3.3.4.2.
3.3.4.4 MJC Ignition Coils. - The MJC generator uses two suppressed
ignition coils mounted on the intake manifold. Normal ignition coil
maintenance should include inspecting and tightening-the terminals and
cleaning them if necessary.
A quick check for possible coil failure can be made by simply discon­
necting the high tension spark plug leads (cyl. 1 or 4 for coil nearest
cyl. 1 -- cyl. 2 or 3 for other coil) See Fig 3.3. H _ Then hold the end
of the leads 1/4 inch from bare engine metal and crank the engine. A
spark between the lead end and the engine indicates the coil is operat ­
ing, although it (one coil or the other) may be weak, which could only
be checked on a tester or by checking resistances. No spark indicates
that the coil, points, or control circuit to the coil
is
defective. Before
condeming the coil if there is no spark, check hi tension lead for volt­
age while cranking the plant and inspect the breaker points.
For further tests of the coil see no _ 1 and 2 under Sect 3. 3.3. 5.
3.3.4.5 MJC Ignition Condensers. - The two condensers are mounted in
a vertical position inside the distributor.
If
they are suspected of being
defective, see Sect 3.3 _3 _4 for testing, and replace
if
necessary. Ca ­
pacitance should be .3 mfd.
3.3.5 SPARK PLUGS.
MJA, MJB, and MJC generating plants use aviation type spark plugs
equipped to accept suppressed ignition leads. Fouled spark plugs indi ­
cate they are too cold. Consult the plant parts catalog for the factory
recommended plug. Remove, clean, and inspect the plugs at regular
intervals.
If
they are in good shape, they can be cleaned on a commer ­
cial plug cleaner and regapped. The spark plug gap should be set at
.025 inch for gasoline fuel.
When spark plug electrodes become excessively worn or
if
the plugs
are damaged, replace them.
When replacing or reinstalling spark plugs, always install new gaskets.