McCulloch PRO MAC 610 - Breaking in a New Engine

3. Before making or checking carburetor adjustments, in-
stall the bar and chain and be sure that the chain is
being lubricated properly. A properly lubricated chain
will throw a fine spray of oil off the nose of the bar when
the chain is moving at operating speeds.
4. Before checking carburetor adjustments, be sure that the
air filter is clean and securely in place on the air box.
5. All engines lose power as altitude increases. This is due
to the "thin" air (less oxygen in the atmosphere at
higher altitudes). The rate of power loss is approximately
3% per 1,000 feet (300 meters) of elevation. Therefore,
an engine will develop only 85% of its sea level power at
an altutude of 5,000 feet (1,500 meters), and only 70%
at 10,000 feet (3,000 meters). Other factors, such as
temperature and humidity, will affect power output also.
Adjustment Procedures
NOTE: The PM 650 has a built-in, automatic high speed
governor. This governor is pre-set at the factory to provide the
best engine RPM for power and overall engine performance,
including best fuel economy. The governor also prevents the
engine from running at excessive RPM's which can cause
severe engine damage. Tampering with the governor is
considered abuse and will void the warranty.®
1. Gently turn the LOW SPEED and HIGH SPEED MIXTURE
NEEDLES in (clockwise) until they seat, then turn both
needles out (counterclockwise) one full turn.
2. Adjust the IDLE SPEED SCREW until the throttle plate is
just slightly open.
3. Start the engine and let it warm up thoroughly at low
speed.
CAUTION: When making carburetor adjustments or
testing the unit for full throttle operation, never run the
engine at full throttle without a cutting load for more than
a few moments. Excessive full throttle operation while
not cutting can cause serious engine damage.
4. Accelerate the engine several times, adjusting the
LOW SPEED MIXTURE NEEDLE to obtain a smooth, rapid
acceleration without hesitation or falter. If the needle is
turned in too far, the engine will hesitate or falter when
accelerated. If the needle is turned out too far, the engine
will run rough and smoke heavily when accelerated.
NOTE: for PM 650 units only, when HIGH SPEED MIX-
TURE NEEDLE is correctly set at 1 to 1-1/8 turns open
(slightly less at altitude), you will notice a lightly surging
RPM at wide open throttle with a free running chain but
not while under a cutting load.
5. Adjust the IDLE SPEED SCREW so that the engine idles
without any chain movement.
6. Check saw performance:
CAUTION: Engine performance is determined by the
cutting speed and ease of operation under load. There-
fore, do not adjust the carburetor for maximum sound
level as this is likely to result in a lean running condition
which can cause engine damage.
A. With the throttle wide open, make a test cut in a log.
If the carburetor is properly adjusted and the chain is
properly sharpened, the saw will cut quickly,
smoothly, and with minimum operator effort.
B. If the engine sounds rough and slows down in the
cut, turn the HIGH SPEED MIXTURE NEEDLE clock-
wise slightly to increase cutting speed and smooth-
ness.
C. If the saw has speed but lacks power to continue a
smooth cut, turn the HIGH SPEED MIXTURE NEEDLE
counterclockwise slightly to increase power.
NOTE: It may take several test cuts to arrive at the most
satisfactory adjustment.
BREAKING IN A NEW ENGINE
Breaking in a new chain saw engine is very important. Run
your engine for its first few minutes at one-third throttle.
Increase speed to about half-throttle and run for a few min-
utes longer. Cut a few limbs or small logs at first. Check
chain tension frequently and use the manual oiler button often.
It is advisable to use a slightly richer fuel mixture during the
break-in period. Turn the high speed mixture needle about
one-eighth turn counterclockwise from the normal preliminary
starting position. After about an hour's operation, turn the
adjusted needle back one-eighth turn clockwise.
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