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DWELL TEST
Up
TM-9-4910-749-10 Test Set Tachometer Dwell (NSN
Next
TM 9-4910-749-10
1-9. PCV TEST
WARNING
a. A defective PCV permits crankcase vapors to
Make sure that the par k i n g b r a k e i s s e t
escape to the atmosphere. This increases air pollu-
tion, and causes rough idling.
(3) Observe the LOW RPM scale (0-1500 RPM).
b. To perform the PCV test do the following:
RESULTS:
Too high-Speed adjusted too fast
Adjust idle speed screw.
(1) Turn the test selector to the LOW RPM
Normal-Speed  correctly  adjusted.
position (See Figure 5).
Too Low-Speed adjusted too slow.
Adjust idle speed screw.
(2) At norms idle speed, pull out the PCV
1-8. IDLE MIXTURE BALANCE TEST
hose assembly from the valve cover of the engine.
WARNING
(3) Place thumb over end of PCV valve while
observing  meter.
P l a c e shift selector in Neutral or Park be-
fore proceeding with this test.
RESULTS: Speed drops 50 RPM or more-PCV ok.
Speed  drops  less  that  50  RPM-PCV
a . Excessive leanness or richness causes a rough
defective. Clean or replace the PCV
operating  engine,  diseling  or  stalling  at  idle.  A
valve and clean the PCV hose.
vacuum gauge can also be used to adjust the idle
mixture.
(4) Reconnect the PCV hose assembly to the
valve cover of the engine.
b. To perform the idle mixture balance test do
the following:
1-10. AIR FILTER TEST
( 1 ) Turn  the test selector switch to LOW RPM
a. A dirty air filter causes an overrich fuel mixture
position (See Figure 5).
resulting in poor fuel economy and loss of power.
(2) At normal idle speed, observe meter and
b. To perform the air filter test do the following:
t u r n idle mixture screw(s) slowly in (clockwise) and/
or out (counter-clockwise) to achieve highest RPM
(1) Turn the test selector to LOW RPM posi-
and smoothest idle operation.
tion (See Figure 5).
R E S U L T S : Too far in - Causes lean mixture and
(2) Remove the air filter and note the RPM
rough idle. Adjust.
reading.
Normal-Runs
smoothly.
No
adjust-
ment needed.
(3) At normal idle speed, with the air filter in
Too far out - Causes rich mixture,
place, note the RPM reading.
rough idle, and poor fuel economy.
Adjust.
R E S U L T S : Minimal RPM Change-Air Filter ok.
Excessive
RPM
Change-Air
Filter
is
(3) After idle mixture is adjusted, readjust idle
dirty
and
restricted.
Replace.
speed.
NOTE
NOTE
For use with waterproof electrical ignition
On many late model emission-controlled
systems, you must use Adapter, Engine
vehicles, limiter caps have been installed
Electric, NSN 4910-00-356-7504 which is
to prevent overrich idle mixtures. Refer to
a c o m p o n e n t : o f A d a p t e r S e t , E n g i n er
specific recommendations of manufac-
turer.
1-3/ (1-4 blank)

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