Onan MJA Series Service Manual page 41

39
FUEL SYSTEM
3.2.7 EXHAUST SYSTEM
The exhaust system is normally supplied by the user, and installed in
the field. However, the importance of correct exhaust system cannot
be overemphasized. A poor or clogged system can cause low power,
over heating and eventual damage. The effect of a poor exhaust system
is to increase the back pressure at the engine, reducing efficiency.
If
excessive back pressure is suspected, check
it
according to the proce­
dure below.
3.2.7.1 TESTING. - Install an adapter Or tee in the exhaust line next to
the manifold. Connect a manometer or pressure gauge to the adapter.
If there is a condensation trap next to the manifold, this can be used for
the manometer connection. Run the plant under full load and observe
the manometer. See Fig 3.2.Mfor maximum values. If the reading is
higher, the exhaust system should either be disassembled and cleaned
or altered to reduce back pressure.
NOTE: Back pressure readings can be taken at no load and maximum
values are shown below, but this isn't as accurate as full load
readings. Take the back pressure readings at full load when ­
ever possible.
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UNITS OF"
MEASUREMENT
FULL
LOAD
NO
LOAD
INCHES
OF
WATER
27
5.1
INCHES
OF
MERCURY 2
3
8
OUNCES 15.60Z 2.90Z
j
INCHES OF
WATER
27 4.7
INCHES OF'
MERCURY
2
I
"3
OUNCES
15.60Z 2.70Z
F1G 3. 2. M - MEASURING EXHAUST BACK PRESSURE