75
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)
NOTE: Perform all jetting changes on a
motorcycle that has been warmed up to proper
operating temperature.
The carburetor on your Cobra motorcycle is
quite adjustable. Figure 49 shows its range of
adjustment and in particular what adjustable
component affects what range of operation
(specifically throttle position).
Figure 49
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