*Engines with four valve cylinder heads.
in the exhaust manifold companion flange and tapping a 1/8" pipe thread.
Check the readings obtained at various speeds (no load) with the specifications in Table 4.
Air Box Pressure
Proper air box pressure is required to maintain sufficient air for combustion and scavenging of the burned gases. Low
air box pressure is caused by a high air inlet restriction, damaged blower rotors, an air leak from the air box (such as a
leaking end plate gasket), or a clogged blower air inlet screen.
Lack of power or black or grey exhaust smoke are indications of low air box pressure.
To check the air box pressure, connect a manometer to an air box drain tube.
Check the readings obtained at various speeds with the specifications in Table 5.
Air Inlet Restriction
Excessive restriction of the air inlet will affect the flow of air to the cylinders and result in poor combustion and lack of
power. Consequently, the restriction must be kept to a minimum considering the size and capacity of the air cleaner. An
obstruction in the air inlet system or dirty or damaged air cleaners will result in a high blower inlet restriction.
The air inlet restriction may be checked with a manometer connected to a fitting in the air intake ducting located 2" above
the air inlet housing. When practicability prevents the insertion of a fitting at this point, the manometer may be connected
to the engine air inlet housing. The restriction at this point should be checked at a specific engine speed. Then the air
cleaner and ducting should be removed from the air inlet housing and the engine again operated at the same speed while
noting the manometer reading.
The difference between the two readings, with and without the air cleaner and ducting, is the actual restriction caused by
the air cleaner and ducting.
Check the normal air intake vacuum at various speeds (at no-load) and compare the results with Table 6.