The early Bronco uses a plastic fuel supply line running from the tank to the mechanical fuel pump and then steel line to the carburetor. A return line is not factory-equipped on carbureted models but is required for EFI conversions. Tom's Offroad carries replacement steel and stainless steel fuel line sets for the 1966–1977 Bronco, along with rubber fuel hose sections and fittings for connections at the pump and carburetor.

Inspect early Bronco fuel lines for damage, pinhole leaks indicated by fuel staining or smell, cracked or swollen rubber sections, and loose or corroded fittings. Any soft spot in a rubber section or rust pitting on steel lines indicates replacement is needed. Fuel leaks are a fire hazard, do not delay inspection or replacement on any truck showing signs of fuel line deterioration.

Yes, stainless steel fuel lines are a worthwhile upgrade for any early Bronco restoration, offering corrosion resistance that will outlast the truck itself. Stainless lines also resist the ethanol content in modern pump gasoline better than steel. Braided stainless fuel hose with AN fittings is popular in performance builds, while seamless stainless hard line is preferred for a factory-clean appearance under the truck.

The factory early Bronco fuel supply line is 5/16-inch diameter, which is adequate for the stock carburetor and mechanical fuel pump. Performance builds with upgraded carburetors or EFI conversions may benefit from upgrading to a 3/8-inch supply line for improved flow, particularly on builds with larger engines or higher fuel demands. The return line on EFI conversions is typically 5/16 inch.

Yes, modern pump gasoline contains up to 10% ethanol (E10), which can degrade original rubber fuel line materials over time, causing swelling and cracking. When replacing any rubber fuel line sections on an early Bronco, use hose specifically rated for ethanol-blended fuels. Stainless or nylon-reinforced fuel hose with ethanol compatibility is the best long-term choice for all rubber sections.