How to Replace Lead Fuel for Old Cars

by Contributor

Older cars may seem simple in comparison to today’s modern masterpieces, but they are much more complicated than you might think. Take the fuel system, for example. The cars of yesterday were designed to operate on leaded fuel and at much higher compression ratios. The fuel of today contains no lead--thus it serves up problems in those older power plants, especially in the form of valve train failure. The remedy? There are a couple of areas where you can improve older vehicles and the use of today’s fuels.


Park the car on a flat, level surface and apply the parking brake. Open the hood.


Adjust the timing. Running an older engine on today’s fuel requires the timing to be retarded a few degrees. Mark the harmonic balancer with chalk on the indicated number of degrees you wish to set the timing at. (This will be an experiment for each particular vehicle, but shoot for 10 to 12 degrees timing from idle and 34 degrees total timing). Loosen the distributor hold-down bolt with a wrench just enough to allow the distributor to be turned. Connect the timing light to your engine's ignition system according to manufacturer's instructions. Start the engine. Turn the distributor until the timing light (when pointed at the harmonic balancer) falls onto the number of degrees timing you wish to operate at. Tighten the hold down bolt and shut the engine off. Remove the timing light and close the hood.


Add a fuel additive. Pour a lead additive into the fuel tank of your vehicle at each fil-up. Follow the manufacturer's instructions as to the proper amount to add.


Replace the carburetor. With the vehicle parked and the parking brake applied, open the hood. Using a wrench, remove the air filter (breather) housing and set aside. Remove the fuel line with a wrench and wrap with a rag to avoid spilling fuel. Unhook throttle linkage by removing clip and rod from the carburetor. Remove the mounting bolts from the carburetor and lift it off of the engine manifold. Replace the gasket and place the new carburetor in place. Tighten the mounting bolts, replace the throttle linkage and fuel line. Replace the air breather assembly. Start the engine and look for fuel leaks. Turn the engine off and close the hood.


  • check Always use the highest-octane-rated fuel you can find for older vehicles. This helps deter detonation and spark knock.
  • check In extreme cases, you may need to have the engine's heads machined for hardened valve seats. Contact a reputable machine shop for this.


  • close Never smoke or use electric lights around an open fuel source.

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