Honda Civic Wagon 4WD 1990 Owner's Manual page 41

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Gasoline
For proper operation of your car's emission controls, your engine is
designed to use unleaded fuel only.
CAUTION:
Using leaded or even low-lead gasoline could damage some of your
emission controls, and also void their coverage under the emission
controls warranty.
Use gasoline from pumps labeled unleaded, with a pump octane
number of 86 or higher. The pump octane number is an average of
the Research (R) octane and Motor (M) octane numbers. Use of a
lower octane gasoline can cause
KNOCK" (a metallic rapping noise), which can lead to engine damage
if severe.
CAUTION:
If you notice steady spark knock while holding a steady speed on a
level road, try changing brands of gasoline. If the spark knock
persists, consult your Honda dealer. Failure to do so is considered
misuse, and misuse is not covered under the New Car Warranty.
Occasionally you may notice light spark knock while accelerating or
driving up hills. This is no cause for concern, it simply means your
engine is running at its most economical.
Gasoline Containing Alcohol
If you decide to use a gasoline containing alcohol ("gasohol"), be
sure its octane rating is at least as high as that recommended for
unleaded gasoline. There are t w o types of
containing ethanol, and that containing methanol. Do not use
gasohol that contains more than 10% ethanol. Do not use gasoline
containing methanol (methyl or wood alcohol) that does not also
contain cosolvents and corrosion inhibitors for methanol. Never use
gasoline containing more than 5% methanol, even if it has
cosolvents and corrosion inhibitors.
persistent, heavy
"gasohol": that
"SPARK