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74
CAUTION:
Proper jetting is very
important for engine performance and engine life.
Symptoms of improper jetting are listed below.
•
Symptoms of incorrect oil or oil / fuel ratio
o
Poor acceleration
o
Misfire at low engine speeds
o
Excessive smoke
o
Spark plug fouling
o
Excessive black oil dripping from exhaust system
•
Symptoms of too rich a fuel mixture
o
Poor acceleration
o
Engine will not ‘rev’ out, blubbers on top
o
Misfire at low engine speeds
o
Excessive smoke
o
Spark plug fouling
o
Wet, black, or overly dark spark plug (when removed for inspection)
•
Symptoms of too lean a fuel mixture
o
Pinging or rattling
o
Erratic acceleration
o
Same actions as running out of fuel
o
High engine temperature
o
White spark plug (when removed for inspection)
NOTE:
When inspecting the spark plug to evaluate jetting, a properly jetted
machine will produce a spark plug that is dry and light tan in color.
Environmental and altitude related mixture adjustments
Condition
Mixture will be
Required adjustment
Cold air
Leaner
Richer
Warm air
Richer
Leaner
Dry air
Leaner
Richer
Very humid air
Richer
Leaner
Low altitude
Standard
None
High altitude
Richer
Leaner
Low barometric pressure
Richer
Leaner
High barometric pressure
Leaner
Richer
NOTE:
Before making any carburetor jetting changes verify that:
o
You are using the proper fuel and oil
o
The fuel is fresh and uncontaminated
o
The oil and fuel have been mixed in the proper ratio
o
The carburetor is clean (no plugged jets)
o
The air filter is properly clean and oiled
o
The float height is within proper specification (proper measuring technique
is described later in this section)