Factors Which Assist Good Carburetion
Ignition spark plug should be set with at least .025" gap. 1\lany are now using .031" gap, and some even use .035". (See also page 1302 for discussion on spark plug gap.)
Interrupter points should be clean and properly set according to manufacturers' specifications. Usually about .015" to .020" gap when the points are wide open, with spark lever retarded when TC mark on flywheel is in line with pointer is the approximate average interruptor setting and timing.
Leaky carburetors are in many instances caused by dirt under the float needle valve.
It can usually be removed by alternately raising and lowering it. from its seat, at the same time giving it a twisting motion with the fingers.
If the dirt is loose or only slightly embedded this will wash it away.
In aggravated cases, hold the needle valve firmly on the scat with the fingers and, with a light tool, gently tap the top of the valve.
The bearing points of the needle valve and of the needle valve seat are highly polished at the factory. Therefore, do not try to regrind the seat as this procedure is in most cases productive of bad results.
If necessary to fit a new needle valve, or needle valve seat, replace both of them with new parts. Never replace one and leave the other in the carburetor. When any parts of the needle valve or float mechanism are replaced use a level test gauge to adjust the fuel level.
If the float is leaky and contains gasoline, the additional weight will cause a high level and flooding condition.
If the needle valve counterweights are worn badly, the float can raise too high and will result in flooding. Turn them over, or replace with new weights.
Never raise or lower the fuel level for the purpose of leaning or enriching the mixture.
If, after stopping the engine, a bit of fuel leaks from the carburetor, do not be alarmed. This is only the fuel drawn up into the carburetor barrel and manifold which, due to insufficient suction, does not get to the cylinders. When the engine is stopped, releasing the suction, this fuel naturally drops and is soon drained off through the small hole in the bottom of the carburetor provided for that purpose.
This is more noticeable in cold than in hot weather. Always close the throttle before shutting off the engine. This will usually eliminate this condition, and in other cases reduce the loss to a minimum.
Hard Starting
See if you have fuel in the carburetor. This can be determined by removing the dust cap and pressing down on the needle valve. If the valve cannot be de-pressed by the finger there is fuel in the carburetor.
In the case of F-type carburetors, remove the float cover to see if fuel is in the bowl.
See if you have a good spark at the spark plugs.
Have throttle lever only slightly open, so as to get full effect of the suction on the idling jet and well.
See if strangler valve closes completely. Check manifold and connections for air leaks.
Be certain starter is turning engine over with sufficient speed to lift fuel to the cylinders (at least 100 r.p.m.).
Check for dirt or water in carburetor and particularly in idling jet.
In cold weather it sometimes happens that water accumulates in the carburetor or fuel line and freezes, thus shutting off the flow of fuel.
Weak compression, riding valves, faulty adjustment of spark plugs and breaker points will make starting hard.
Do not flood the engine with gas. If you do, release the strangler, open the throttle half way and turn the engine over. This will dilute the mixture in the cylinders to a point where it will ignite.
Too much gasoline consumption may result from one or several causes:
Check carburetor adjustment.
Check ignition adjustment.
Check brake adjustment.
Check fuel connections and carburetor for leaks. Check hot air tubing connections.
Check strangler adjustment.
Check condition and amount of oil in engine, transmission, rear axle, wheel bearings, universal joints, etc.
The dimensions, given in inches, are the measurement from the top of the machined surface of the float bowl to the fuel itself on the following models and sizes of carburetors:
Models CV14, CV20, CV20C, CV20L, CV20M, i,"; model CV22F, g4"; models IA, 1.5, L6, L6T, L7, L7T, L8, 1,5"; models 034, 04, 05, Q4C, Q5C, 41"; Model Q6C, l h"; model T3, a4"; models T3 „ T4, T4X, T4XF, T4F, T5F, T5XF, 44”; models S4, S4BF, 1J4, 44"; models S5, S6, U5, U6, 4)"; models USF, U5FL, U5FW, U5FR, 1,z"; models UL5, UL6,
Models SV5, SV6, SV7, SV8, 1,4 "; models ST4, ST4B, ST4T, ST5, a4"; model T5T, a4"; models T4DS, T4XD, 41"; model US52, ill".
Models HF2 4K, HF3K, HF3KC, HF3A-B, a4"; models HF3 4, FF3 4F, HF4A, HF4B, HF5H, a4"; models HP4, HP5, 4i"; models HP6A, IIP6B, 1A:,"; models HR20, HR20AM, HR26A, HT3, l"; model HT4F, a4"; models HT5HF, HU4A,
Models 04D, 05D, 06D, 07D, 08D, 1"; models ER20F, ER26A, 444"; model V4B-SV4, a$".
Model 48DC, l"; models SLGS, SL6L, SL7R, SLRS, 1,5".
To make adjustment, it is necessary to unsolder the needle-valve collar and move it up or down on the float needle valve and then resolder; moving collar away from pointed end slightly lowers the level and toward pointed end raises the level. Models ST and SV can be adjusted by bending the float arm, but this is not considered good practice. All Zenith carburetors bear a scratch-awl mark on the side of float chamber which indicates the gasoline level.
Level test gauge: On all models except ST and SV it is necessary to use a level test gauge to set the fuel level properly, be-cause when the float cover is removed the gasoline level drops (not. on ST and SV models). Three gauges are required to fit all makes of Zenith carburetors (one each for models L, 0, and T) and the price is $2.50 each. (Can be obtained of Zenith-Detroit Corp., Detroit, Mich., or at Zenith service stations.)

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Carburetor Manuals: Zenith