Zenith Carburettor Handbook

Zenith Carburetor (Baverey's System) 13th Edition April 1923

Difficulty in Starting the Engine (1) Page 8
FIRST:
Be certain that the throttle is just open 'a crack' and that the strangler valve is closed tight.
SECOND:
See if there is fuel in the carburetor. If the needle valve is off its seat and can easily be depressed with the finger, the float chamber is empty, and the fuel system should be checked to determine if there is fuel in the tank above the level of the carburetor, or if the fuel valve is closed. If there is sufficient fuel in the tank and the fuel valve is open, take off fuel line and Filter Body of the Carburettor and assure yourself they are not stopped up with dirt.
THIRD:
Take off a spark plug lead and hold it about 1/8" away from spark plug terminal; with ignition switch on, crank the motor and see if a spark jumps across the gap thus formed. If no spark occurs check up the ignition system.
LEAKS IN MANIFOLD & ITS CONNECTIONS:
These leaks commonly occur at the joints, and are caused by faulty gaskets, by neglect to place gaskets, or by faulty machining of the manifold flanges preventing their being drawn tight together all around the passage. (The best gasket to use is one of soft, tough and compressible material. Rubber should not be used as gasolene has a deteriorating effect upon it. The gaskets should not be more than 1/16" thick. Thicker gaskets may cause the flanges to become sprung, thus causing another leak.) In the case of tubing manifolds leaks are sometimes found along the seams. In cast manifolds sand holes sometimes occur. To find these leaks use soapy water, or oil, covering the suspected points with it and crank the engine. Disturbance of this film or a hissing sound will indicate a leak.
WORN VALVE STEMS & GUIDES:
These commonly occur in older engines are often a source of mysterious trouble until detected and replaced. In case no leaks are found in the manifold, or connections, try squirting gasolene around the valve guides and crank the engine. Too much importance cannot be attached to air leaks as a seemingly insignificant leak will cause serious difficulty in starting the engine and will also seriously impair the running of the engine under closed throttle conditions.

When all of the foregoing points have been attended to and the motor still refuses to start, try the following:-
Prime the engine cylinders through the priming cocks, or, if priming cocks are not provided, take out the spark plugs and prime through the spark plug holes; do not overdo it, a few drops in each cylinder will suffice. Crank the engine and if it starts immediately but stops as soon as the priming charge is burned out remove the Idling Device from the Carburetor and see if it is stopped up with dirt.
If the engine will not start at all remove spark plugs and examine them carefully for cracked porcelains, faulty gaskets, improperly adjusted points etc. The plugs should not have a gap smaller than 0.020" or greater than 0.025". However, if the batteries or the magneto be weak, starting may sometimes be accomplished by setting the spark plug points a bit closer together, say 0.015" to 0.018". It is desirable in such a case that the batteries or magneto be replaced or repaired.
Other, but uncommon causes of difficult starting are:-
Lack of oil around the pistons, allowing leaks by the piston rings.
In old Spark Plugs the porcelains may be carbonized, or may have very fine fractures allowing a leakage of current. In the case of mica plugs the mica may become oil soaked.

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