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Zenith Service Guide

IMPORTANT POINTS

The correct working of the ZENITH Carburetter can only be assured when it is not tampered with in any way. The jets must not be reamered out or hammered up, and the hints given in this booklet must be strictly adhered to. A ZENITH Carburetter, properly fitted, can be tuned up in a few hours, but when badly fitted, the tuning up becomes impossible.
The number stamped under the main jet and compensating jet corresponds, as a rule, to the bore of the jets in hundredths of millimetres. For example, a main jet marked 125 has an orifice with a theoretical diameter of 1.25mm, and one marked 85 should measure 0.85mm. All jets are calibrated on a B. & B. Mark II flowmeter, but sometimes customers specially request that the jets should be stamped with the number corresponding to their flow in cubic centimetres of petrol per minute, based on the Mark II flowmeter. In this case, the jets are specially marked with "c/c" after the number, and we shall be pleased to send a list of equivalents to interested customers.
All the jets are very carefully gauged to pass a certain quantity of fuel in a stated time, and therefore two jets bearing the same number pass exactly the same quantity. It is essential that they should not be altered under any circumstances. The standard markings on our jets run in fives, so that a size larger jet than 80 would be 85, and a size smaller would be 75, and so on. The higher the number, the larger the jet.

For the names of the different parts of the Carburetter, please refer to the sectional drawings on pages 14 and 15.


NATURE OF THE FUEL USED

The ZENITH Carburetter is supplied already adjusted for use with petrol spirits of densities between 700° and 750°. Carburettors thus adjusted may be used with benzole without altering the setting. The level, however, will be lower in the carburetter due to the increase in density, but this difference in level is necessary and usually precludes any modification of the jets. Never weight the float or make alterations to the level when using heavy spirits, but one size smaller jets may often be used to advantage.
When using comparatively high-density spirit such as Benzole, it is crucial to install a very efficient heating apparatus to properly vapourize the heavier fuel. Paraffin can also be employed with the ZENITH Carburetter, provided an efficient vapouriser is fitted between the carburetter and the cylinders, and arrangements are made to run the engine until hot on petrol, after which it can be switched over to paraffin. The key to success with paraffin is to properly vapourize the fuel, and in this regard, it can be said that a proper vapouriser is one in which the inlet pipe passes virtually inside the exhaust pipe.


FITTING THE CARBURETTER

POSITION

The vertical type of ZENITH Carburetter must be placed in an accessible position to quickly take out the jets and unscrew the petrol union. A space of a few inches should therefore be left below the carburetter, which should be placed sufficiently low to ensure a plentiful supply of petrol, even when the car is on a steep hill. As a rule, the bottom of the petrol tank should be at least * inches above the top of the float chamber.
For cars on which the tank is placed under the seat, the carburetter must be placed fairly low. It is always preferable to place the float chamber towards the front of the car so that when going downhill, the petrol does not run out of the jets. These precautions are not necessary for the horizontal type of carburettors, as they can only be fitted in one position, which is against the inlet port on the cylinder. Their accessibility is assured, but on the other hand, they can only be fitted to cars where the petrol is supplied under pressure, by vacuum tank, or where the tank is sufficiently high on the dash. These horizontal carburettors are only suitable for monobloc engines with one inlet port, with the valves on the opposite side. If an inlet pipe is used, the vertical carburetter is more suitable, and this type must only be adopted. Also, take care to ensure that the carburetter is fitted quite horizontally, so that when the car is on level road, the carburetter is also level and does not slope.

CONTROL

The control, being worked by the accelerator pedal or by a lever on the steering wheel, should be as direct and rigid as possible. It should be arranged in such a manner that the complete movement of the accelerator or hand lever corresponds to the complete movement of the throttle lever on the carburetter. It is also advisable to arrange the controls so that a large movement of the pedal or lever corresponds to a small movement of the throttle lever on the carburetter. This provides a greater flexibility of control.
Stiffness must be avoided, so that when acceleration is effected by the pedal and the pedal is released, the throttle in the carburetter will return to its former position. In addition to the accelerator pedal spring, it is desirable to fit another small spring on the throttle lever to take up any slackness or play in the connections. The later types of ZENITH Carburettors are fitted with adjustable throttle levers, which enable them to be set in any position.



CONCERNING THE INLET PIPE

The shape, size, and disposition of the inlet pipe are crucial factors when fitting a vertical ZENITH Carburetter. The internal diameter of the horizontal branch leading to the cylinder ports can be the same size as the ports themselves, but the vertical portion should be tapered from a few millimetres smaller than the outlet of the carburetter to the same size as the branch.
hints and tips 1
Hints and Tips 1
Fig 1 shows a sketch of a well-designed inlet pipe. We have found the following sizes of piping (internal dimensions) to be the most suitable for the various carburettors of our make. Sudden changes in the speed of the gas cause a considerable loss of charge, and it is necessary that internal variations of size should be progressive.

It was formerly thought necessary to have pipes of equal length from the carburetter to the different cylinder ports. However, experience has shown that pipes of different lengths have very little influence on cylinder filling, but that bends are the cause of considerable loss of charge.

Figs. 3 and 4 show two examples of well-designed piping, while Fig. 2 shows a pipe that, although serving the same purpose, gives inferior results.
Hints and tips 2

Hints and Tips 2
Dips and pockets where petrol vapour can condense should also be avoided (Fig. 5).
 hints and tips 3
 
Hints and Tips 3
If the piping branches to distribute the mixture to several cylinders, the branching should occur no less than 3 or 4 inches from the carburetter. Drawn copper inlet pipes are much better than cast ones, as the latter have a rough internal surface that restricts the free flow of gas. These remarks also apply to the inlet passages inside the cylinder block when a horizontal carburetter is used. The general layout of the inlet pipe or passages from the carburetter to the valves should always correspond as closely as possible to the conditions laid down.

We offer a series of flanges, bends, T-pieces, etc., for the fitting of the vertical type of carburettors. Particulars can be sent on application, while our copper-smithing department is always available to make complete pipes or special fittings.
We also carry a large number of special inlet pipes and adaptors to fit the ZENITH Carburetter to many well-known car makes.

HEATING

The horizontal type of carburetter does away with the need of a heating device, as it can only be fitted where there is a certain length of induction pipe inside the cylinder casting, which is heated by the water circulation.
To ensure the perfect working of the vertical carburettors, the air entering the carburetter (or better still, the mixture itself) must be heated.
It is impossible to correctly tune up a vertical carburetter which does not possess one or the other of these heating systems. The majority of the difficulties encountered by customers in tuning up their engines are caused by the absence of, or inadequacy of, the heating device. These difficulties are caused by the condensation of petrol vapour in the induction pipe. It is indispensable that this condensation should be avoided in order to regulate the slow running, ensure a quick pick-up, and obtain an even running of the engine.
Three Methods of Heating:

  1. By means of the water circulation.

  2. By means of the exhaust gases.

  3. By means of the hot air taken into the carburetter.


HEATING BY HOT AIR ENTERING THE CARBURETTER

This system, which should only be used when the water circulation is by thermo-syphon, consists of leading into the Carburetter air that has been warmed by contact with the exhaust pipe. This is effected by placing a muff around the exhaust pipe, from which muff a pipe is taken to the air port on the Carburetter. In certain cases, the hot air may be taken from the enclosed space around the valves as shown in Fig. 10, but this method is not very efficient and should only be adopted when it is impossible to employ any other system.
hints and tips 4
 
 
Fig. 11 shows the best method of heating by means of hot air, and we can supply all the necessary parts for this fitting.
Avoid using too long a pipe, and ensure that the air does not have to descend in order to get to the carburetter. To regulate the quantity of hot air, a revolving sleeve is placed on the pipe just before it reaches the carburetter. This sleeve has slots cut in it which correspond to slots cut in the pipe, allowing cold air to be admitted as required.
 

FIXING THE CARBURETTER AND FLANGES

  • If the inlet piping is very rigid, the carburetter can be suspended from it by means of two bolts. However, if the induction pipe is neither very short nor very rigid, and the carburetter tends to shake about, it must be supported in some way.

  • This support could be fixed at one end by one of the bolts passing through the flange, and at the other end by one of the bolts on the engine or frame.

  • The flange washer (of fibre, asbestos, etc.) should be of even thickness so that the flanges fit snugly together and allow no air to pass between them. The same remark applies to all joints in the piping.

THE PETROL PIPE AND FILTER

It is absolutely necessary to have a filter somewhere on the petrol pipe between the main tank and the Carburetter in order to prevent the jets from becoming blocked with impurities that may come through with the petrol.
To this end, we have placed on the market our new plate-type filter, which will fit between the Carburetter and the tank. This filter will absolutely remove all impurities from the petrol, definitely preventing the jets from becoming choked up under any circumstances. Details of this filter will be gladly sent on application.
 hints and tips 5
When the petrol is fed by gravity from the main tank or from a vacuum tank to the Carburetter, care should be taken that the petrol pipe slopes gently from the tank to the Carburetter. There should be no ups and downs, sharp bends, or pockets in the pipe, as air would likely collect and cause an airlock. The petrol pipe should not touch anything hot, such as the exhaust pipe or silencer, as this would cause the petrol to vaporize and cause a gas lock in the petrol pipe. The petrol pipe should also not touch any parts of the chassis unless necessary, as constant rubbing against anything hard can wear a hole in the pipe. It is generally advisable to put a twist in the pipe to allow for vibration between the Carburetter and the tank. A well-laid-out petrol system with a filter is shown in Fig. 12.
In order to clean the gauze filter under the float chamber, the petrol pipe is first disconnected, and then the brass hexagon is unscrewed from the Carburetter using an ordinary spanner. When this hexagonal adaptor is completely unscrewed and withdrawn from the carburetter, it will bring with it the filter tube. The tube should be thoroughly cleaned by washing in petrol, taking care not to damage the gauze. It is then replaced in the Carburetter in a similar manner.


THE AIR STRANGLER

The later models of Zenith Carburetters are fitted with an air strangler, the purpose of which is to facilitate starting when the engine is cold. This strangler should be connected to the dashboard by means of a rod or wire, but very often a Bowden wire is employed.
Great care should be taken in its installation to ensure that when the control on the dashboard is released, the strangler on the Carburetter will fly open to the fully opened position. Stiffness in the control will cause the air strangler to stick in a partially closed position, which will upset the general running of the car and increase the consumption. The strangler is only useful for starting purposes when the engine is cold, and must not be used as an air adjustment when the car is running on the road. The correct use of the strangler is described later under the heading "Starting."

We give below the method of connecting up the Bowden wire control to the strangler, using the dashboard control that we supply.
hints and tip 6

INSTRUCTIONS FOR FITTING STRANGLER CONTROL

  1. Make bracket H and fix it to any convenient bolt or stud in a rigid manner.

  2. Fix "Tee" barrel stop G to bracket, in line with the hole in the strangler lever.

  3. Fit dashboard control L, with knob in the "open" position: Grease wire D well, slide it on casing J, and pull wire through stop G until all end play in the casing is taken up. (If necessary, cut casing to the required length.)

  4. Mark off the length of wire D required. Solder wire for 1" on each side of this place (Fig. 1) to prevent the wire from unraveling when cut. Cut the wire at the center of the soldered portion with a chisel or fine file.

  5. Slip shackle B on the wire, then lightly solder nipple C (Fig. 2).

  6. Test pull, and if correct, spray the end of the wire over the nipple (Fig. 3). Finish off with a blob of solder (Fig. 4).

  7. Fit the shackle to the hole in the strangler lever with a split pin. Slacken locknut F, and take up any end play in the casing J by unscrewing plain stop E. Tighten locknut F.

Avoid sharp bends in the casing. It is better to err on the long side when measuring wire or casing.

TAKING DOWN THE ZENITH CARBURETTER


THE FLOAT CHAMBER:

In the vertical type of Carburetter, pull back the spring button which holds the cover in place, and carefully lift off the cover together with the needle and balance weights. The edge of the cover is milled to ensure a good grip, but care should be taken to avoid bending the needle. After the cover is removed, it is easy to take out the float using the needle, or a hooked piece of wire, which is placed down the center hole.
Often, a small piece is filed out of the edge of the float chamber cover, which must align with either the screw holding the spring or the body of the Carburetter. Care should be taken when replacing the float chamber cover to ensure this cut-out portion is in the correct position. After inserting the needle into the float, if the cover is turned round, it will generally fall into the correct position.
In some horizontal types of Carburetters, the center knob is unscrewed one turn. Then, by turning the cover slightly, it can be removed easily.
hints and tips 7

THE CHOKE TUBE:

The choke tube is a cylindrical piece of metal placed in the body of the Carburetter, around the jets, to cause the rush of air necessary to form a good mixture and regulate the quantity of air entering the Carburetter.
In the vertical type of Carburetter, the throttle and spindle must be taken out before the choke tube can be removed. To do this, remove the set screw which fixes the throttle on the spindle, take the throttle between the thumb and first finger, and pull the spindle out. After this, loosen the pressure screws holding the choke tube in place, and it will then come out quite easily by turning the Carburetter upside down.

If this is not the case, owing to the choke tube or Carburetter having received a blow, it can be removed as shown in Fig. 14. First, unscrew the main jet and the main jet cover. Then place a metal washer (e.g., a halfpenny) against the choke tube, and force it out with a thin rod passing through the main jet hole. Care should be taken not to damage the thread of the main jet and cover.
When replacing the choke tube, make sure that the narrowest internal part is downwards, and that the groove around it rests on the ledge cut for that purpose in the body of the Carburetter (Fig. 15). Tighten the pressure screws to hold the choke tube in place, then put back the spindle and throttle. It is important that the throttle is properly refitted, and when it is correctly replaced, the lower edge, when fully shut, should just cover the outlet from the slow-running tube. The number stamped on the throttle should be uppermost.
In the horizontal type of Carburetter, it is much easier to take out the choke tube. First, unscrew the dome air intake or air strangler on the back of the Carburetter. Then, take out the main jet below, unscrew the main jet cover, and by turning it to one side, the choke tube will pull out of the Carburetter with the main jet cover. The choke tube is installed at the same time as the jet cover.
 
hints and tips 8

TAKING OUT THE JETS

A jet key is sent out with each Carburetter for the purpose of removing the jets. The hexagonal nuts below the jets must be first removed using an ordinary spanner. Once this is done, the jets can be unscrewed with the special jet key. When replacing the jets, ensure they have a washer on them, and that it is properly seated on the shoulder.
We also supply a special box spanner for removing the plug under the jets. Price: 2/2 post free.
Section of Horizontal Carburetter
 hints and tips 9
Section of Vertical Carburetter
 Hints And Tips 10
 

TUNING UP THE CARBURETTER

Each Carburetter is sent out with a main jet, a compensating jet, choke tube, and main jet cover best suited for that particular engine according to our experience. The combination of these four parts constitutes what we call a setting. The Zenith Carburetter being automatic in principle, it is necessary to adjust it to suit the particular engine on which it is to work to obtain all the advantages it affords in terms of flexibility, power, and economy. We would also mention that the Carburetter need only be adjusted once, as it cannot vary or alter on its own.
If we receive correct details of the engine when the Carburetter is ordered, the setting put in the Carburetter is usually the correct one, because it has been carefully tested on similar cars in the past. A Carburetter with this setting should not be altered unless the running is unsatisfactory, which is often due to other parts of the engine being out of adjustment. However, since individual engines may vary slightly, we think it advisable to make a few remarks on the general adjustment of the Carburetter.
 
 
 hints and tips 11


ADJUSTMENT PROCEDURE:

The Zenith is adjusted by determining the correct sizes of choke tube (Fig. 16), main jet (Fig. 17), compensating jet (Fig. 18), and by adjusting the slow-running tube (Figs. 21 to 23).
Normally, the choke tube regulates the quantity of air entering the Carburetter and controls the velocity. The main jet is most influential at high speeds, while the compensator corrects the irregularities of the main jet at low speed. This compensator has a significant effect at low pulling speeds such as when climbing hills or accelerating.
Most Carburettors supplied by us are fitted with an open main jet cover (Fig. 19), but sometimes, for old two-cylinder engines where the suction stroke occurs at irregular intervals, we fit a dome cap (Fig. 20).
The standard open main jet cover has an internal diameter of 3.3 mm, but sometimes a slight improvement is found for small engines in acceleration by fitting a main jet cover with a slightly smaller orifice, such as 3.2 mm or even 3.1 mm. The size of the main jet cover is stamped on one side of the hexagon at the base of the cover. A fuller description of the principle of the Zenith will be gladly sent upon application.
hints and tips 12
 

STARTING UP:

With a cold engine, the best method is as follows: Close the Air Strangler, open the throttle slightly until a sucking noise is heard when the engine is cranked over. This indicates that the petrol is being sucked through the slow-running tube. If the ignition and valves are in order, the engine should start immediately.
As soon as the engine has started, open the air strangler slightly. After a few minutes, when the engine has warmed up, the strangler can probably be opened fully.
If the engine starts readily but stops shortly afterward, it usually indicates that the throttle is not opened sufficiently. If the throttle is opened too much, it will always cause difficulty in starting.
(Further hints on starting will be found on page 22.)


SLOW RUNNING:

Several systems of slow-running adjustment have been applied to the Zenith Carburetter, with the latest methods in use since 1914. The adjustment of slow running depends on setting the throttle to obtain the correct quantity of mixture and adjusting the slow-running tube for the proper quality of the mixture. A stop screw is provided on the throttle lever and should be adjusted so that the engine runs at its lowest speed when warm, without stalling on sudden deceleration.
Once this adjustment is made, the slow-running tube should be adjusted as described below. Slow running, which may seem like a matter of personal preference, significantly affects acceleration. Therefore, it is crucial to adjust slow running as carefully as possible.
hints and tips 13
 
The slow-running tubes (Figs. 21 and 23) are pushed into the Carburetter and held in place by means of a screw. To remove them, simply loosen the screw and pull the tube out. If the tube is tightly fixed, it can be pried up with a screwdriver, inserting the point under the knob “B” or under the nut “X” when this is loosened. Use a convenient part of the Carburetter, such as the throttle boss, as a fulcrum.
In the type shown in Fig. 22, the tube is screwed into the Carburetter and must be removed with a special hexagonal key that is supplied with the Carburetter. The strength of the mixture is regulated by altering the relative position of the male and female cones "A" and "G."

  • Male Cone "A": This takes the form of a conical jet. When the female cone "G" is placed close to this jet, the suction increases, resulting in a richer mixture.

  • If the adjustment portion "G" is unscrewed, the distance between "A" and "G" increases, reducing the suction on "A" and, thus, weakening the mixture.

The size of the male conical jet "A" is stamped on the bottom of the tube. If, after adjusting "A" and "G" close together, the mixture is still not rich enough, a larger orifice "A" may be required. If, after unscrewing "G" two or three complete turns, the mixture remains too rich, then a smaller jet is necessary.
In the type shown in Fig. 21, it is necessary to remove the complete tube from the Carburetter. When removed, the part "Q" can be unscrewed or screwed up. Holding part "B" in the left hand, screw part "Q" clockwise to make the mixture richer, and anti-clockwise to weaken it.
In the type shown in Fig. 22, which is only used with horizontal Carburetters, first remove the cap "N." Then turn the screw "B" left or right with a screwdriver, in the same manner (clockwise to enrich, anti-clockwise to weaken).
For the latest type, as shown in Fig. 23, the adjustment can be made while the engine is running. Loosen nut "X," then screw the knob "B" clockwise to make the mixture richer and vice versa. Once the correct position is found, the knob can be locked in place with nut "X."
There is no standard position for the adjustment of the slow-running tube, as this varies for each engine. As a general rule, it will be somewhere between the fully closed position (when the female cone touches the male cone, the richest position) and two complete turns unscrewed. After the slow-running tube has been adjusted, it may be necessary to make a small adjustment to the stop screw on the throttle lever.

 

GENERAL RUNNING

In the following, we deal with specific defects in running and their remedies, but the following general remarks on tuning are also useful:

  • Choke Tube Too Large: Generally, this results in poor acceleration under all conditions.

  • Choke Tube Too Small: The engine picks up well, but maximum speed cannot be obtained due to the choke tube restricting the quantity of air entering the Carburetter.

  • Main Jet Too Large: This causes heavy petrol consumption and irregular running at medium and high speeds. It's sometimes found that the same speed is achieved with two jets of different sizes. The smallest jet should always be chosen for better economy.

  • Main Jet Too Small: This causes a loss of power, popping back during acceleration, and the engine will run harshly, possibly running a bit warm.

  • Compensating Jet Too Large: Causes sluggish acceleration and irregular running at low speeds.

  • Compensating Jet Too Small: Results in missing during acceleration and possibly knocking when pulling hard at low speeds.


HOW TO WRITE FOR PARTICULARS RE: TUNING UP

To receive accurate assistance, please provide the following details:

  1. H.P. make and year of car.

  2. Number of cylinders.

  3. Bore and stroke of the engine.

  4. Number of Carburetter used (mention all letters and figures stamped on the side of the float chamber).

  5. The current setting (number on main jet, compensator, and choke tube).

  6. Whether a heating device is installed, and if so, the type.

Additionally, please mention any other relevant particulars, such as existing issues, to help us respond more effectively.



COMMON RUNNING TROUBLES AND THEIR REMEDIES

DIFFICULT STARTING WHEN COLD

This is generally caused by the throttle not being set correctly.

Starting Procedure:

  1. Close the air strangler.

  2. Shut the throttle fully back to the stop screw (the position where the engine runs slowly out of gear when warm).

  3. With the ignition switched off, crank the engine over 6 or so times either by hand or with the self-starter.

  4. Then, open the throttle by 1/16th to 1/8th of an inch, keeping the strangler shut, and switch on the ignition.

This should allow the engine to start readily. The cranking without ignition helps free the engine and primes it with the right mixture for starting.

  • Throttle Position: The best position is generally just above the slow-running position when warm. A few trials will help determine the best throttle position for easy starting.

  • In Very Cold Weather: Starting may be facilitated by slightly flooding the Carburetter.


Potential Causes for Difficult Cold Starts:

  1. No Air Strangler fitted or existing one not closing properly. We can supply a loose strangler for earlier types of Carburetters. Ensure the strangler control allows full closure.

  2. Slow-Running Tube choked up: Clean Jet "A."

  3. Slow-Running Tube adjusted too weakly: Turn the adjustment knob clockwise for a richer mixture.

  4. Air Leakage between Carburetter and Cylinders: Check all inlet pipe joints, valve caps, and sparking plugs. Worn inlet valve guides may allow air leakage.

  5. Magneto Retarded too much or inefficient at low rpm: This should be carefully checked.

  6. Spark Plug Points too far apart: Slightly closer points often improve starting.



DIFFICULT STARTING WHEN HOT

  1. Slow running tube adjusted too richly: Adjust the knob anti-clockwise.

  2. Carburetter flooded or air strangler closed: An excess of petrol causes difficult starting when the engine is hot.

  3. Throttle not open sufficiently: Adjust the stop screw to open the throttle a little more.


BAD SLOW RUNNING

If the slow-running tube and stop screw have been properly adjusted, but slow running is still poor:

  1. Air leakage between carburettors and cylinders: Check the mentioned points. If a vacuum-tank, servo brake, or windscreen wipers are fitted, check air connections carefully.

  2. Magneto is inefficient at low speeds or advanced too much: Have this checked thoroughly.

  3. Spark Plug Points too far apart: Adjust the gap.

  4. Inlet Valve Tappets badly or unevenly adjusted: Carefully set tappets.

  5. Uneven Compression in Cylinders: Have the valves ground in.

  6. Inlet Pipe or Passages not sufficiently heated: Petrol vapour may condense inside the unheated passages, causing irregular slow running. Improve heating by fitting a hot air pipe or cleaning out the jacket if one exists.

  7. Throttle Spindle or Throttle Worn: After prolonged use, the throttle spindle and throttle can wear, disrupting slow running. It's best to send the Carburetter back for overhauling.


ENGINE STOPS ON DECELERATION

  1. Slow-Running Tube choked up: Remove and clean.

  2. Slow-Running Tube adjusted too weakly: Set this for a richer mixture.

  3. Inlet Valve Tappets unevenly adjusted: These must be set properly.

  4. Throttle loose on its Spindle: Tighten the locking screw holding the throttle to the spindle.

  5. Stop Screw on Throttle Lever improperly adjusted: Set this screw so the throttle always returns to the best slow-running position.


ACCELERATION IS BAD OR THERE IS HESITATION IN PICKING UP SPEED

  1. Inlet pipe or passages insufficiently heated: Petrol vapour condenses inside, causing hesitation when accelerating. Ensure better heating of the inlet pipe or passages.
  2. Compensating Jet too large or too small: Try different compensating jets.
  3. Choke Tube too large: Try a smaller choke tube without changing the jets.
  4. Slow-Running Tube not correctly adjusted: Adjust the slow-running tube carefully for even running.
  5. Uneven Distribution of the Mixture: This could be due to the shape of the inlet pipe or passages.