All 1973-79 Hondas are designed to run on regular gasoline. High octane (premium) gasoline is not required. This is permitted because the engines uses the CVCC combustion system, thereby avoiding the catalytic converter. The octane number is used as a measure of the anti-knock properties of a gasoline and the use of a higher octane gasoline than that which is necessary to prevent engine knock is simply a waste of money. If your Honda does knock (usually heard as a pinging noise), it is probably a matter of improper ignition timing, in which case you should check Engine Performance and Tune-up for the proper adjustment procedure. You might also want to check that the EGR system is functioning properly (see Emission Controls ).
The 1980-83 models use a catalytic converter even if the engine uses the CVCC system. This is because of increasingly stringent emissions standards. While unleaded gas is usually more expensive than leaded, there are many side benefits, including better fuel economy, less dirt in the engine oil and longer exhaust system life. Since the use of leaded fuel will damage the catalytic converter, it does not pay to attempt to bypass the narrow filler opening for the fuel tank and run the vehicle on leaded fuel. Little more than a single tankful will render the converter ineffective and may cause it to clog the exhaust system and affect engine operation.
You should be careful to use quality fuels having an octane rating of 86 when measured by the R/M method, which averages Research and Motor octane ratings. Too low an octane rating will produce combustion knock, which will prove to be damaging to the engine over a long period. Always buy fuel from a reputable dealer, preferably where a regular volume is pumped so that the fuel is always fresh.