more than once around or one turn from its seat.

Set stove heat and damper heat as previously instructed above. Pull out choker to closed position and start engine in usual manner. As soon as engine has fired release choker three-fourths of way in. Run until engine has warmed up then push choker all the way in, remembering to never use choker longer than necessary, as when not needed it has a tendency to foul up engine and ruin the lubricating oil in the crank case.

Next, set air screw for good idle by either turning to the right a little or backing out to the left as the needs of the engine require, remembering that first of all, the needle must be set as described. With the needle so set and the engine warmed up, the adjustment of the air screw for proper idling is easily accomplished by using a little care. If the air screw is turned in too tight, the motor will roll. If the air screw is not tight enough, the motor will hesitate and perhaps stop entirely. To make a nice clean adjustment for idle, first having set needle as described, turn air screw in quarter of a turn at a time until engine, does roll; then turn back to the left until engine hesitates, indicating that mixture has too much air and is too lean; next turn air screw in to the right three or four notches at a time until engine runs smoothly. This accomplished (and it is very easy to do by proceeding as directed above) the proper adjustment for the entire range of the engine will have been attained, thus insuring the best economy and power.

MODEL "S" MARVEL CARBURETER

STANDARD EQUIPMENT 1923–24 Series 691 Nash Sixes

If the engine idles too fast with throttle closed, the latter may be adjusted by means of the throttle lever adjusting screw.

RICH MIXTURE

An over-rich mixture will cause the engine speed to fluctuate through more or less regular periods from high to low speeds; the engine will seem to be mis-firing and there will be noticeable a strong odor, as well as, usually, a heavy black smoke from the exhaust.

LEAN MIXTURE

The best adjustment is obtained with the fuel and air valves set as described. It must be remembered that too lean a mixture as well as an over rich mixture causes over-heating and loss of power and is not as economical as an adjustment which provides just the proper proportion of gasoline and air.

CAUTION

It must be remembered that the low speed needle has been carefully calibrated to notch in disc handle and guide post above it, at the factory and that in making an adjustment that the needle must be so set and the rest of the adjusting done with the air screw as described, never varying from described needle setting unless in extreme cold weather, when a little more gas may be carried, or turning off a little when casing head gas is used in hot weather.

MARVEL CARBURETER
MODEL "S"

Nash Series 691 Sixes Parts Price List