Durant 1928-30 Motor Tune-Up

The most important operations in a Durant motor tune-up are ignition timing, spark plug gap setting and distributor point adjustment. If difficulty is experienced at idling speeds on cars equipped with Tillotson carburetors, check for defective by-pass tube (see Auxiliary By-pass Tube in section Following Tune-Up Operations). The carburetor is the last unit that should be checked, all other adjustments such as timing, spark plugs and contact point settings should be made before changing or adjusting the carburetor.

Tune-Up Operations

1. Clean and adjust distributor and spark plug points.
2. Check timing chain for slack; adjust if necessary.
Note: Care should be exercised not to get the timing chain too tight. Adjust the chain to a point just below a hum. If timing chain is loose, proper results cannot be obtained when timing the motor.
3. Check the ignition timing; adjust if necessary.
4. Adjust the valve tappets and free up valves.
5. Clean gas line strainers and screens. Also check gas lines for loose fittings.
6. Check fan and generator belts. Adjust if necessary,
7. Tighten water pump nut. This operation is only necessary when packing gland is leaking.
8. Adjust carburetor, clean if necessary.
9. Road test car.
Note: The ignition should never be advanced beyond a point where a spark knock occurs except under full load conditions.

Ragged Idle

Ignition Timing.--A condition of poor idle may be caused by the ignition timing being advanced too far. The symptoms are similar to those
caused by a too rich carburetor mixture and are especially noticeable at idling speed.
Spark Plug Gap.--A poor idling condition on Durant motors may be caused by spark plug gaps being set too far apart. The recommended
setting is .027" for all models of Durant.
Distributor Points.--When tuning a motor it is important that the distributor points be thoroughly cleaned and squared up: Dirty distributor contacts may create a condition of motor performance very similar to a rich carburetor mixture condition. The motor will run poorly at low speed and cut out at high speed.
High Vacuum in Manifold.--A poor idling condition especially noticeable on deceleration, may be caused by a high vacuum in tile manifold over the throttle on Durant cars equipped with Steamberg Model U carburetors. The car may idle properly on the service floor but when the motor is accelerated to full open throttle and then decelerated suddenly to full closed throttle, a tendency to load and Roll wall be noticed. In extreme cases the motor may even die on deceleration. The ear owner generally complains that the motor dies in traffic. To correct this trouble, drill a No. 52 hole through the throttle valve butterfly about $/16" in toward the center of the carburetor throat opposite the idle discharge opening.
Caution: The throttle valve should never be drilled unless the trouble cannot be corrected by reducing the size o£ the main metering jet or Economizer by-pass.

Auxiliary By-Pass Tube Defective

If trouble is experienced in obtaining an idling adjustment on Tillotson carburetors used on Durant cars, the trouble may be caused by a defective or split auxiliary by-pass sleeve (A) Fig. 9. A poor idling condition may also be caused by dirt collecting in the bottom of the auxiliary by-pass or idling tube (B). If the trouble should be caused by dirt in the bottom of the idling tube, see that the filter screen around the bottom of the tube is thoroughly

In the operation of forming the auxiliary by-pass sleeve (A) Fig. 1 the end of the sleeve may crystallize and split or fold under when the. By-pass tube is seated. Invariably a leak at this point will cause the air vent chamber surrounding the tube proper to flood and proper air bleed is prevented. Showing method of flaring by-pass tubes used on Tillotson carburetors. In the left hand view (A) two by-pass tubes are shown, that were damaged in flaring or during the operation of installation. When the by-pass tubes are damaged in this manner carburetor operation will be affected. Durant 1928-30

Extreme care should be exercised in the fitting of by-pass tube. By fitting we mean the clearance between the hole in the upper half of the carburetor body casting and the outside diameter of the by-pass tube. When air is allowed to leak at the point immediately on top of the tube the mixture is thinned and the low speed adjustment is rendered inoperative in proportion to the amount of air, which passes around the tube. By using a small tapered punch having a point angle of 30° those tubes found to be undersize can be flared as desired.

Lack of Power

Improper adjustment of the Metering or Economizer Needle--Lack of power at high speeds on all models of Durant’s equipped with Tillotson SP and V types of carburetors may be caused by improper adjustment of the economizer or metering needle. The nut which is pinned to the lift needle can be adjusted when necessary. This adjustment should allow a lift and fall of approximately 3/32". The clearance between the bottom of the nut and the contact point of the lever fork should be about .040". In replacing cotter pins be sure that the ends of the pins after being bent do not ride or touch the body casting thus interfering with tile free action of the lift and fall of the needle.

Low Gasoline Mileage

Auxiliary Needle Valve Held Open-On cars equipped with Stromberg Model U carburetors, low gasoline mileage may be caused by the auxiliary control lever cam riding the auxiliary control lever thus holding the auxiliary needle valve open. To correct, set the auxiliary control lever cam so that there is approximately 1/16" clearance between the cam and the auxiliary control lever. Also check to see that the auxiliary control lever. Fulcrum screw does not bind and that the lever works freely.

Gasoline Leaks

Loose Main Nozzle (Tillotson Carburetors)-A gasoline leak, which may be confused with a leaky float valve ma}, develop on all models of Tillotson used as equipment on Durant cars. The trouble is generally indicated by a slow dripping of gasoline or a wet carburetor body. The main nozzle is screwed into its passage against a gasket. The trouble may be caused by the jet loosening up and working down on the thread away from the gasket thus causing a leak at the gasket
between the shoulder and the carburetor body at the top of the nozzle. To correct, remove the adjusting screw assembly at the bottom of the carburetor and screw the jet up tightly against the gasket. Care should be exercised not to confuse this condition of trouble with a leak that is caused by incorrect float level adjustment. If the gasoline level in the float bowl is too high, gasoline will have a tendency to seep over the top of the main nozzle thus causing a leaky condition, which may be indicated by a slow dripping of gasoline or a wet carburetor body. If the trouble is caused by the wrong gasoline level, correct by resetting the float to the correct height. (See float level adjustment under Carburetor Specifications).

Leaky Channel Plugs

A gasoline leak which may be confused with a leaky float valve may develop on all models of Tillotson used on Durant models. The trouble is generally indicated by a slow dripping of gasoline or a wet carburetor body. To correct this trouble, remove the carburetor air horn and tighten up the channel plugs with a screwdriver.

Information Donated by Carol Rush