Higher temperature expands the air with its
resultant reduced density.
Higher humidity reduces the amount of oxy-
gen in the air by so much of the water vapor
in the same air.
Lower atmospheric pressure (at a high alti-
tude) reduces the density of the air.
After warming up the engine equipped with the
standard type carburetor(s) and spark plug(s),
run two or three laps of the circuit and check
the smooth operation of the engine and discol-
oration of spark plug(s).
É Over burned (too lean)
Ê Oil fouled (too rich)
7 - 2
T U N
Condition of spark plug
Insulator is dry and burnt
Insulator is whitish.
Insulator is sooty and wet.