Honda 1990 Accord Sedan Owner's Manual page 57

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 oc-
tane 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 persistent,
heavy "spark 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 ac-
celerating 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 recommend-
ed for unleaded gasoline. There are two types of "gasohol":
that 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.