Harbor Freight Tools 93547 - Manual (Page 5)

Page 5 For technical questions, please call 1‑800‑444‑3353. SKU 93547
goes dry and the engines dies, the
fuel pump is working properly.
4. Turn ignition off and reconnect
fuel line to the fuel pump.
Vacuum Testing
1. With the engine off, connect the
Vacuum / Pressure Gauge (1) as close
as possible to the intake manifold.
Use the Rubber Hose (2) and the
various adapters as needed. Do
not kink Rubber Hose. Do not allow
air leaks. Engines with two intake
manifolds have to be tested separately.
2. Start the engine and let it idle until
the engine temperature reaches its
normal operating temperature.
3. Adjust throttle butterfly valve
and set idling speed to get
a smooth engine idle.
4. Take vacuum reading from the Vacuum
/ Pressure Gauge (1). Readings will
vary depending on altitude.
At idle engine speed, with a properly
adjusted carburetor, the gauge pointer
will remain fixed between 17 and 22
IN/Hg (the green zone on the gauge),
19.5, optimum.
A slow, fluctuation between 14 and
22 IN/Hg indicates that the carburetor
needs adjustment, or there are
other engine problems. Refer to the
vehicle’s service manual for normal and
abnormal readings, and adjustment or
repair procedures.
Other possible engine problems
can be diagnosed as follows:
• When the gauge pressure drops
intermittently about 4 IN/Hg, it could be
an indication of sticky valves. Remove
the Rubber Hose (2), add a few drops
of penetration oil to the manifold
and test again. If the valves stop
sticking, valves need to be cleaned.
• A constant low reading on the gauge
could indicate a burnt valve(s).
• If the gauge pointer pulsates
rapidly when the engine speed is
raised, it could indicate weak valve
springs or poorly seated valves.
• At idle engine speed the gauge pointer
pulsates, but at higher speeds the
pointer is steady, this could be an
indication of loose valve stem guides.
• When the gauge pointer drops slowly
when the engine is sped up several
times in secession, this could indicate
a clogged muffler. An unblocked
muffler will cause the gauge pointer
to momentarily drop to zero.
• When the gauge pointer remains
at 12 IN/Hg at any engine speed it
could indicate late valve timing.
• Test the choke by closing throttle all
the way and starting the engine. The
gauge pointer should immediately rise
to 22 IN/Hg (green zone). If the gauge
pointer stays around 3 to 6 IN/Hg this
may indicate a burnt riser tube, or the
failure of the throttle valve to close.
There could also be air leaks in the
intake manifold system.