Tractor Principles / The Action, Mechanism, Handling, Care, Maintenance and Repair of the Gas Engine Tractor

by Roger B. Whitman

With adjustable air valves it is usual to adjust for idling, that is, the slowest speed at which the engine will run steadily without load, and then to make any necessary additional adjustment for full speed and power.

If a carburetor cannot be adjusted by following the usual methods, trouble may be looked for, and this may be in the carburetor itself, in the fuel supply, or in the intake manifold, taking for granted, of course, that the engine is in proper condition and that the ignition system is operating correctly.

Dirt under the float valve will prevent the valve from seating, and the level in the float chamber will be too high, so that the mixture is too rich. Lifting the valve from its seat will let fuel rush through, and loose particles will thus be washed away. If dirt is ground into the valve and seat, or if these parts are worn, the valve must be reseated, which is done by turning the valve against its seat with light pressure, the end of the valve being gently tapped with a light hammer. Under no conditions use a grinding compound, for the particles would become imbedded in the soft metal and would ruin the valve.

Other causes of flooding are a bent valve, the sticking of the float pivot, and the soaking of fuel into the cork float, which is thereby made too heavy to float properly. The remedy is to dry it, and then to give it three coats of shellac.

A frequent cause of trouble is dirt in the pipe from the tank to the carburetor. While there may not be enough dirt to prevent the engine from running slowly, it is sufficient to prevent the flow of sufficient fuel for full power. A strainer is always provided, and this should be drained every day; if this is not done frequently, dirt will work its way through.

A grain of sand in the spray nozzle will choke it, and every precaution should be taken to keep this from happening, as well as the other troubles that dirt brings. The best precaution is to strain the fuel through chamois leather, or, if this is not obtainable, through a very fine metal wire screen.

In fuel systems that use a pump, the sticking of the check valves, and the leaking of the pump through poor packing, will cut down the supply of fuel.

If air can leak into the carburetor or intake manifold, the proportions of the mixture will be altered. To test for leaks, run the engine, and with a squirt can squirt gasoline on the joints or other places that are suspected of leaking air. If there is a leak, the gasoline can be seen being sucked in.

Air must enter the tank to take the place of the fuel that flows out, and this is provided for by a small hole drilled in the tank-filling cap. If this hole becomes stopped up, the fuel will not flow, and the engine will come to a stop. There is a similar hole in the top of the float bowl of most carburetors, and this also must be kept open.

An engine is always started on gasoline, for that will form a mixture when it is cold. Before switching to kerosene the engine must be hot, and this will take several minutes of running on gasoline.