GAS GIMMICKS

A good tune up of your carburetor, points and plugs will do more for your gas mileage than most of the gimmicks now offered for sale. Plugs can do no more than explode all of the mixture in the compression space, and if they do that, you don't need the super duper jet age miracles at $5 a piece. Premium (higher octane) gasoline prevents selfignition (knocking), but does not, in itself, improve gas mileage.

The main points in driving for maximum gas mileage are minimum acceleration, minimum deceleration, and coasting at every chance. (It is, however, illegal in most states to kill the engine during coasting, and some states prohibit coasting altogether.)

If you are very serious about driving for optimum mileage, you need an indicator that measures instantaneous mileage. Meters labeled "fuel consumption," such as found on some 1974 Pontiacs, measure the vacuum in the manifold, which is proportional to the consumption, but not to the mileage. An instantaneous gas mileage indicator is now sold by the J.C. Whitney Co. (1917 Archer Ave., Chicago, IL 60616) for about $30; however, installation is not easy, as the meter must be geared to the speedometer and the gas line must be cut to install a sensor.