PERIODIC MAINTENANCE, ENGINE TUNE-UP PROCEDURES AND STORAGE

LUBRICATION

OIL ENTERS AND LEAVES THE PUMP AT POINT A. THE OIL FLOW IS GOVERNED BY OIL PASSAGES IN THE ECCENTRIC. AS THE PUMP EXTENDS, OIL FLOWS INTO CHAMBER B. WHEN THE PUMP PLUNGER IS FORCED IN, THE OIL IS PUSHED OUT OF CHAMBER B, THROUGH PASSAGE A, AND IS DIRECTED THROUGH THE CAMSHAFT.

The oil in the crankcase serves five functions:

1. It helps cool the engine by removing heat from the cylinder and moving parts.

2. It cleans by rinsing particles from the cylinder and moving parts.

3. It seals the rings to the cylinder wall.

4. It reduces friction by serving as a slippery film between all moving parts.

5. It protects the machined parts from rust and corrosion.

The oil is circulated in the engine by several methods. Some engines use a dipper attached to the connecting rod which dips into the oil as the connecting rod moves. The oil is splashed so that all points within the block are constantly sprayed with oil.

The oil slinger used on some engines is driven by the camshaft. As the slinger rotates, "ears" on the slinger throw oil throughout the inside of the engine.

Various styles of oil pumps have been used in the lubrication systems of small engines. The pumps normally are submersed in oil and direct oil to the connecting rod and main bearings by tubes or orifices in the discharge tube. The other parts of the engine are lubricated by the oil which is "thrown off" the connecting rod and crankshaft.

When an engine that employs an oil pump is being overhauled, the pump should be checked carefully for wear. If the pump shows wear, replace the main components or the complete pump assembly.

OIL AND OIL CHANGE

The oil level should be checked before starting the engine and after every 5 or 6 hours of operation. The oil level should be maintained to the full mark as recommended by the engine manufacturer. When checking or adding oil, care should be taken to prevent any dust or dirt from entering the oil filler. The engine oil should be changed when it is warm so that all the oil will drain from the engine. Change the oil at least after every 25 hours of engine operation.

Use the weight and grade oil recommended by the manufacturer. The use of additives is not necessary unless specified by the manufacturer.

If manufacturer data are not available, use the following guide in selecting oil:

Service rating SC, SD, or SE Type Detergent

Summer SAE 30 or 10W-30

Winter SAE SW-20 or 10W-30

COOLING SYSTEM

Excess heat from the small engine is removed by air circulated over the engine. Air is drawn in through the screen in the shroud which covers the fly wheel. The spinning flywheel throws the air outward and the shroud directs it across tile engine.

It is very important that the air intake screen and the fins on the engine be kept clean. If dust and grass are permitted to build up over these areas, the air flow is restricted. Such restriction of the air flow can cause the engine to run "hot."

Blockage of just one passage can create a "hot spot" which can cause scratched piston rings, a scored cylinder wall, and scoring of the piston.

The engine shrouding should always be in place when the engine is operated, Without the shrouding, the air is not directed over the engine and the engine will overheat.

The screen over the air inlet area should be brushed frequently with a stiff-bristled brush to remove accumulated grass and dust.

The shroud should be periodically removed from the engine and the accumulated dust and chaff should be removed by blowing around the fins with compressed air.

When the engine is being serviced, care must be taken to prevent breakage of the cooling fins on the engine block and cylinder head. These fins provide necessary "extra" surface area to remove the excess heat from the engine.

Broken flywheel fins or blades reduce the amount of air circulated over the engine and cause the flywheel to be out of balance. If any flywheel fins are broken or missing, the flywheel should be replaced.

The fuel system and ignition timing can also affect engine cooling. If the fuel mixture is lean, the engine will tend to run hot. Late ignition timing will also increase the operating temperature of the engine.

SPARK PLUG SERVICE

First remove the spark plug wire and attach it to a good engine ground. Use a deep well spark plug socket or box end wrench to loosen the plug. Use care not to damage the plug. Loosen the plug about one turn. Spir. the engine four to five revolutions to blow out the carbon that may have been knocked loose when the plug was loosened. Blow away any trash, dirt, and caked oil from the area around the plug on the outside of the engine. Remove the spark plug from the engine.

INSPECT THE PLUG

The condition of the plug gives some clues to the condition and operation of the engine.

Normal. If the plug has only slightly worn electrodes and a very light coating of tan or gray deposits, it may be cleaned, regapped, and reinstalled.

Carbon Fouled. Fluffy, black deposits are a result of over-rich carbu-retion or excessive idling. If electrode wear is only slight, the plug may be cleaned and reinstalled. Be sure to correct the condition that caused the carbon fouling. BE SURE THAT IT IS THE CORRECT PLUG FOR THE ENGINE.

Oil Fouled. Wet, black, oily deposits indicate that oil is leaking past the rings or valve stems. Unless the engine condition allowing oil to enter the combustion chamber is corrected, a new plug will soon become fouled too. An engine overhaul may be necessary to obtain satisfactory service.

Blistered Insulator. A burnt or blistered insulator is the result of overheating. Using the wrong spark plug, low-octane fuel, incorrect timing, bad valves, and cooling system obstructions are common causes of overheating. Correct the cause of overheating and replace with a new spark plug.

DO NOT CLEAN SPARK PLUGS WITH ABRASIVE CLEANERS Blasting the plug with abrasives quickly erodes the insulator nose which changes the heat range of the plug. Any deposits that are not readily removed with a wire brush may be scraped away lightly with a pen knife. If excessive deposits are present or if any question exists as to whether or not the plug should be replaced, replace it, A spark plug is a minor expense for the major role it plays in engine performance.

GAP THE NEWSPARK PLUG

New spark plugs are not preset. Check the engine manufacturer's specifications for the correct setting. The correct setting is .025-.030 for most small gas engines. Use a wire spark plug feeler gauge because a flat feeler gauge can give erroneous readings as shown on the opposite page.

REPLACE SPARK PLUG

If the new plug does not screw in easily by hand, clean the threads so that the plug does screw in easily. Then tighten with a torque wrench, if available, to the manufacturer's specifications. If a torque wrench is not available, tighten down finger tight against the new gasket and then turn another one-third turn. This should partially collapse the gasket but not completely smash it. Do not overtighten. Remember that the spark plug has steel threads and the engine head is most likely aluminum or cast iron.

THE IGNITION CIRCUIT

The purpose of the ignition circuit is to create a spark to ignite the compressed air-fuel mixture at exactly the right time. In order to do this, a very high voltage is needed to cause -m electric current to jump the gap between the spark plug electrodes. The duration or intensity of this small lightning bolt is not important because the compressed atr-fuet mixture is highly volatile and will be readily ignited if the conditions are correct.

The ignition system consists of the following components:

• Permanent magnet (in the flywheel)
• Armature-coil assembly
• Breaker points

Condenser Spark plug

As the magnet in the flywheel passes the coi! armature, the moving magnet sets up a current flow in the primary winding of the coil. This current is also traveling through the breaker points. As the breaker points open, interrupting the current flow, the electrical power is transferred magnetically to the coil's secondary winding at a very high voltage. This voltage travels to the spark plug where it jumps the spark plug electrodes igniting the air-fuel mixture. As the points open, a small spark occurs across the points. Since the points open several thousand times each minute, they would soon burn up. The condenser helps absorb this spark and thus acts to increase point life.

PARTS OF THE IGNITION SYSTEM

The FLYWHEEL MAGNET moves rapidly past the coil assembly causing current flow in the coil primary winding.

The ARMATURE-COIL ASSEMBLY consists of the laminated steel armature and the primary and secondary winding.

The BREAKER POINTS are operated by the crankshaft. They close just before the flywheel magnet passes the coil completing the primary winding circuit. The points open just as current flow in the primary is at maximum causing the power to be transferred magnetically (induced) in the secondary at a much higher voltage to fire the plug.

The CONDENSER is connected across (in parallel with) the points to help reduce arcing of the points which increases point life.

ELECTRICAL TERMS

VOLTAGE (volts) is the pressure which causes current to flow. In this sense, it is no different from the pressure that pushes water through a pipe. If you increase the pressure in a water system, more water will flow. If you increase the voltage in an electrical circuit, more current will flow.

CURRENT is the moving of electrons in a wire. This is electricity. Just as water moves in a pipe, electrons flow in a wire. This flow of electrons is called current. The amount of current that is flowing is called amperes (amps) and is measured with an ammeter.

If a faucet has 40 pounds of pressure, the amount of water flowing depends on how much the faucet is opened and on the length of the hose that is connected to the faucet. When a 1-1/2 volt battery is used, the amount of current that flows depends on what is connected to the battery. The wire used must be large enough to easily carry that amount of current. Both the headlights and the dash lights on a car operate from 12 volts. Obviously, the headlights allow more current flow and require larger wire. When the voltage is fixed, as when using a battery, the load determines the amount of current that must flow to get the work done. Opening a faucet wider allows more water to flow and does a better job of blasting off dirt. More work is being done. A larger light bulb allows more current to flow and produces more light.

A spark plug simply creates a gap in the electrical circuit. Current flows easily along the wire to the plug but cannot easily jump the gap. A lot of push (voltage) is needed to cause the current to jump. Usually the voltage required to fire the plug at idle speed is about 6,000 volts and may require as high as 10,000 volts on a small engine under load. High-compression auto engines may require in excess of 16,000 volts under load.

ELECTRICAL FUNDAMENTALS

Tlte following are basic rules that one must comprehend if the basic magneto is to be understood. Study them carefully.

1. Moving a magnet past a wire causes an electrical current to flow in the wire if it is part of a complete circuit.

2. Moving a magnet past a coil made up of several turns of wire will produce a much stronger current flow because the current induced in each turn of wire will add to the total output.

3. Current flowing in a wire causes a magnetic field to surround the wire. The strength of this field depends directiy on the amount of current flowing through it.

4. If the wire is wrapped to make a coil, the strength of the magnetic field of each turn of wire adds to the field next to it, proiuciug a stronger magnet. Adding more turns of wire adds to the strength of the magnetic field.

Figure A shows a current meter (ammeter) connected to a loop of wire. Moving the magnet rapidly causes a very small current to flow in the wire which causes the needle to deflect. Wrapping several turns of wire on a coil makes the current flow much stronger. The current flow induced in each turn of the coil adds to the current flow induced in all of the other turns on the coil to produce a strong current flow.

If a battery is connected to a complete circuit, the current flowing will cause a magnetic field to surround the wire. The more current that is flowing, the stronger the magnetic field. By passing the current through a coil made up of several turns of wire, the magnetic strength of each loop of wire adds to the others making a stronger magnetic field (Figure C).

IGNITION PRIMARY CIRCUIT

The primary or low-voltage circuit consists of the fly wheel magnet, breaker points, condenser, and the coil primary winding. The primary winding usually consists of Kss than 200 turns of coated copper wire wound on the laminated armature. Note that one lead is connected to the armature on one of the mounting hosts which connects it to the engine ground. The other lead from th"! primary winding goes to the breaker points. The condenser is connected across or in parallel with the breaker points. Its only purpose is to prevent arcing of the points, thus increasing point life.

Notice that when the breaker points are closed, there is a complete circuit from the engine ground through the coil primary winding, through the breaker points, to the engine ground. Since both ends of the coi! primary are now connected to the engine ground, a complete circuit now exists. Current will tlow through the ground as if the two ends of the primary winding were connected directly together.

As the piston is nearing TDC on the compression stroke, the breaker points close making a complete primary circuit. The flywheel magnet passes rapidly bringing primary current to maximum. Since the current flow in the primary winding is at maximum, a strong, concentrated magnetic field will surround the primary winding.

Just before the piston reaches TDC (the manufacturer determines the exact number of degrees before TDC) the breaker points open to stop all current flow in the primary circuit. This causes the magnetic field to suddenly collapse. The condenser absorbs a small amount of the current flow in order to prevent point arcing as the points open.

PRODUCING SECONDARY VOLTAGE

FIRING SEQUENCE

1. The points close, making the primary a complete circuit.

2. The flywheel magnet passes, creating current flow in the primary winding.

3. The current flow in the primary winding produces a strong, concentrated magnetic field which surrounds both the primary and secondary windings.

4. The points open, collapsing the magnetic field across the secondary winding.

5. The collapsing magnetic field induces several thousand volts in the secondary winding to fire the spark plug.

PRODUCING SECONDARY VOLTAGE

The coil's secondary winding is wrapped around the primary winding. One end of the secondary winding is connected to the ground, usually along with the lead from the primary winding which goes to the ground. The other secondary lead goes to the spark plug. 

The secondary winding consists of approximately 10,000 turns of very fine wire, usually about 60 times more turns than on the primary winding. The wire need not be large since we are concerned in the secondary with creating a very high voltage to push current across the spark plug gap. A very smalt amount of current is needed.

Since the secondary winding is wound around the primary winding, the magnetic field surrounding the primary winding is also surrounding and saturating the secondary winding. When the points open, the primary magnetic field collapses rapidly. The field collapses across the secondary winding. 

The collapsing magnetic field is a rapidly moving magnet moving past the secondary winding. This collapsing magnet tries to induce current flow in the secondary winding but because of the spark plug gap, a complete circuit does not exist. Since current cannot flow, voltage builds up.

The voltage builds up until it is great enough to jump the spark plug gap, that is, if the coil can build up enough voltage! This is why the secondary winding is made up of several thousand turns of wire. A small voltage push is created in each turn of wire by the collapsing magnetic field. 

The voltage of all the turns is added together to create from 10,000 to 12,000 volts to jump the spark plug gap. The spark occurs at the plug when the points open, collapsing the primary magnetic field across the secondary winding which produces the voltage to push current across the spark plug gap.

FLYWHEEL REMOVAL

In order to service the points on most models -flywheel must be removed. Flywheels are usually made of aluminum or east iron and can be easily warped or cracked. The utmost care must be used in removing the flywheel. Since the flywheel magnet must travel very close to the armature, a warped or cracked flywheel will cause a weak spark or no spark at all.

The flywheel is fitted on the tapered crankshaft with a key. The flywheel is pressed onto the crankshaft taper and held there by a nut or a threaded starter clutch. The first job is to remote, the nut or starter clutch. Use a belt type starter holder as shown in Figure A or a flywheel tool as shown in Figure B or C to hold the flywheel to remove the nut. 

DO NOT hold the flywheel with a screwdriver through the cooling fins. If the cooling fins are broken oft', serious loss of cooling capacity will occur and the flywheel will become unbalanced and cause vibration and bearing damage. DO NOT try to hold the crankshaft on the power take-offend with a pipe wrench, vise grip, or similar tool because damage to the crankshaft could occur.

Use a socket to remove the nut as shown in Figure A, If necessary to remove the starter clutch, use a special starter clutch tool. DO NOT use a hammer on the ears of the starter clutch. If the special tool is not available, make a tool that; wilt engage at least two of the ears on the starter clutch. On some engines, the flywheel nut has left-hand threads. Check threads carefully if there is any doubt about which way to turn the nut. After the nut is removed, the next

job is to free the fly wheei from the crankshaft taper. Pulling or prying will result in a damaged flywheel. The shock of a sharp blow from a steel hammer is the best way to loosen the taper fit.

NEVER STRIKE THE CRANKSHAFT WITH A HAMMER 

Hitting the crankshaft directly with a hammer will result in damaged threads, a broken crankshaft, or a swollen starter clutch shaft. Also, when shock is used to remove the flywheel, care should be taken that the impact is not placed on the engine's main bearings. The best method is for one person to hold the engine approximately one-fourth inch above the workbench. The engine should be held by gripping the flywheel firmly as shown in Figure D.

A second person places a first hammer on the crankshaft end squarely using the nut flush with the end of the crankshaft in order to protect the threads. Strike the first hammer with a second hammer to deliver the shock to the crankshaft end. Strike the second hammer with a strong, solid blow. One good blow will do what several light taps cannot do. HIT IT!

WEAR SAFETY GLASSES OR FACE SHIELD

Fragments from either the hammers or the crankshaft are extremely dangerous.

INSPECT FLYWHEEL AND KEY

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Handle the flywheel carefully! Do not drop it or lay it near large motors or electromagnets such as a generator armature growler. Be sure to locate the key which keyed the flywheel to the crankshaft and store it where it will not be lost.

CHECK THE FLYWHEEL FOR CRACKS

Check the surface of the flywheel for cracks. Check for cracks inside the hub near the key way. If the flywheel is cracked or if the keyway is worn excessively, the flywheel should be replaced.

CHECK THE FLYWHEEL MAGNET

Since (the flywheel magnet is the source of power for the flywheel magneto ignition system, it must have full strength. An unmagnetized screwdriver shoitid be strongly attracted to the flywheel magnet, if possible, compare with a new flywheel or other good flywheel magnet. Some flywheel magnets are replaceable, but on others the whole flywheel must be replaced. Newer flywheel magnets seldom lose their magnetism unless dropped, heated, or exposed to strong AC magnetic fields.

CHECK THE FLYWHEEL KEY

Some engines, especially lawn mower engines, use an aluminum key to keep the flywheel properly secured to the crankshaft. This is to help absorb the flywheel momentum in case the blade strikes an immovable object. With such a sudden stop, the momentum of the flywheel would tend to snap the crankshaft'. Sometimes the key will shear or partially shear as shown at left.''Replace the key with a new aluminum key. DO NOT replace an aluminum key with a steel key,

BREAKER POINTS

Breaker points are relatively inexpensive and easy to change. Considerable care must be used in this task in order to do the job properly. Loss of spark, weak spark, and incorrect spark timing can result from improper point installation. Remember that the spark occurs at the plug when the points open the primary circuit. Setting the breaker points incorrectly will result in improperly set ignition timing.

First, identify the type breaker point and condenser set used. It will probably be one of the two types shown at the left. Note that on one type the condenser is mounted outside the breaker point box. On the other type the condenser acts as the stationary contact point.

When ordering the new contact points, be sure to have the engine brand, model number, type number, and serial number.

Sometimes it is recommended that breaker points be cleaned and readjusted. However, since new points and condenser are relatively inexpensive and since a number of problems can be introduced during the cleaning operation, new points are recommended whenever the engine is dismantled to this point unless, of course, the points have been changed recently.

Sanding or filing will introduce foreign matter to the breaker point area and could prevent the points from making contact or prevent them from opening properly. Many new contact point sets are plated and the cleaning process merely removes the plating. Point life will be very short once the plating is removed.

Note that on the type illustrated above on the opposite page the movable point is opened by a removable cam on the crankshaft. If this cam is removed, as it would be to remove the crankshaft from the engine, note which way the cam came off. If the cam falls off or if you cannot remember which way it came off, consult the manufacturer's manual before replacing the cam because the flywheel, when tightened, may crack if the cam is replaced backward. Also, the points could be badly out of time if the cam is reversed.

REPLACE BREAKER POINTS

1. Secure new breaker points and condenser. Be sure to obtain the following information:

Engine brand_______________

Model number_______________

Type number_______________

Serial number_______________

2. Remove the breaker point box cover. Make a sketch of the breaker points and condenser. Use the illustration on the opposite page as a sample. Carefully indicate the number of wires and the connection point of each wire.

3. Determine the correct setting of the breaker point gap. Refer to manufacturer's specifications. For engines under 7 hp this is usually ,020 inches.

4. Check the condition of the old points.

5. Check the gap of the old points.

6. Remove and replace the points and condenser. Place a tiny amount of lubricant on the breaker cam.

7. Align the new breaker points so that they come together squarely and without overhang. Usually the stationary contact can be adjusted. If necessary, use pliers to bend to the correct alignment. Turn the crankshaft several times to make sure that the alignment is correct,

8. Adjust the gap. Turn the crankshaft until the points are open maximum, Use the correct feeler gauge as shown at left and move the stationary contact until only a light drag is felt as the feeler gauge is moved through the contact area. Remove the feeler gauge and recheck to make sure that the points are not being pushed open as the feeler gauge enters the contact area.

9. Clean the new contacts. Open the points and insert a small piece of hard, white, lint free paper. Move the paper back and forth through the contact area to remove any dust or oil film from the contact area. Be sure to open the points before removing the paper so that no fragments of the paper will be torn off in the contact area.

10. Recheck wiring.

11. Replace the breaker point box cover. Use a small amount of sealer such as Permatex to seal around wires and where the cover seats. The life of the points depends on a clean atmosphere.

ADJUST ARMATURE AIR GAP

On an engine whose armature is mounted outside the flywheel as shown on the opposite page, the air gap between the armature and the flywheel must be adjusted properly.

REMOVE THE ARMATURE FROM THE ENGINE

Remove the screws holding the armature-coil assembly to the engine. Use the correct size ignition wrench or nut driver to remove the screws. Do not use pliers because the screw heads may be damaged.

CLEAN THE COOLING FINS BEHIND THE ARMATURE

If the engine is not going to be dismantled further, clean the cooling fins on the engine block behind the armature before replacing the armature.

CLEAN THE ARMATURE

Use a piece of sandpaper or emery paper to clean the armature laminations. Rust will bridge the gap between the laminations and reduce the coil efficiency. Sand all of the exposed lamination area. Coat the sanded area with a plastic protection spray or light film of grease.

REPLACE AND ADJUST THE ARMATURE

Mount the armature on the engine block. Raise the armature as high as possible and tighten one screw to hold it. Secure a piece of shim stock of the correct thickness. Check the manufacturer's specifications for the correct air gap. Usually this gap wilt be set approximately 0.010 inch. Hard paper such as magazine covers may be used,

Add layers to get the correct thickness. See the section on measuring devices for micrometer operation to measure the thickness of the shim. Do not use a feeler gauge to set the armature air gap. Loosen the screw holding the armature and lower the armature against the shim. Tighten all screws and remove the shim.

On most smaller models, engines having the armature mounted outside the flywheel do not require timing. The only adjustment for timing is at the breaker points. Make sure that the breaker points are set correctly on this type engine.

IGNITION TIMING

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Engines having the armature-coil assembly mounted under the flywheel usually must have the ignition timing adjusted. The various manufacturers prescribe different techniques for the exact timing. Some types have timing marks on the armature and on the engine block. If these are used, it is a simple matter to align the marks and tighten the armature down. On this type, as with the externally mounted armature, the timing accuracy depends on the correct breaker point setting to tire the spark plug at exactly the right time. Adjust the breaker points carefully.

Other engines rely upon finding top dead center (TDC) of piston travel and then moving the piston a specified distance before top dead center (BTDC) to locate the exact point in piston travel that the points should open.

FIND TDC

To find TDC, find the point at which the piston stops moving up and starts moving down. Study the upper illustration on the opposite page. Note that as the crankshaft passed TDC, there is a short distance of crankshaft travel which results in no piston movement. On most engines this point can be found by removing the spark plug and inserting a dial indicator or small machinist's rule. If the cylinder head is removed, the machinist's rule may be used from the top of the block. TDC is halfway between the point the piston stops moving up and begins moving downward.

CONSULT MANUFACTURER'S SPECIFICATIONS Some manufacturers give a distance before top dead center in terms of piston travel. This distance is usually given in thousandths of an inch, such as .060 BTDC. Turn the crankshaft backward until the piston moves the specified distance.

Other manufacturers give a number of crankshaft degrees before top dead center. After TDC is located, the crankshaft must be turned backward the specified number of degrees. A protractor or degree indicating wheel may be used to determine the number of degrees. If the flywheel fins are evenly spaced, as they are on some engines, count the number of cooling fins and devide into 360° to determine the number of degrees between each cooling fin. 

Replace the flywheel carefully and turn the crankshaft backward the specified number of degrees and remove the flywheel. Be very careful not to move the crankshaft while removing the flywheel.

DETERMINE WHEN THE POINTS OPEN

After the crankshaft has been brought to the correct number of degrees BTDC or thousandths of an inch BTDC, the armature-breaker point assembly is adjusted until the points are just opening. Exactly when the points break electrical contact can be determined by using an ohmmeter as shown on the opposite page. All wires must be disconnected for this test. A test lamp and battery may be used instead of the ohmmeter.

PARTS OF THE ELECTRONIC IGNITION

AN ELECTRONIC SWITCH TURNED ON BY THE OUTPUT OF THE TRIGGER COIL

The INPUT COIL is similar to the primary winding in the conventional armature. As the flywheel magnet passes the input coil, current flow is induced in the coil windings. Th? current will charge the capacitor.

The CAPACITOR is a device that will absorb and store electrical energy for a short time. When the flywheel magnet passes the input coil, the capacitor will become charged.

A DIODE is an electrical check valve, ft allows current to flow in only one direction. In this circuit it allows current to flow to the capacitor, charging the capacitor. The electrical energy is then trapped in the capacitor because the diode will not allow it to go back througn the coil.

The SILICON CONTROLLED RECTIFIER (SCR) is an electronic switch. It has no moving parts but normally acts as an open switch to electrical current.

The switch (SCR) is turned ON by a small voltage applied to the gate connection.

The TRIGGER COIL provides the gate voltage to turn ON the SCR. After the magnet passes the input coil which charges the capacitor, it then passes the trigger coil which turns on the SCR allowing the capacitor to discharge through the transformer primary winding. The trigger coil is the timing device since the signal (voltage) to fire (turn on) the SCR i« provided by the trigger coil.

The PULSE TRANSFORMER is similiar to the coil in that it has a primary winding which will buiid up a strong, concentrated magnetic field when current passes through it and a secondary winding made up of several thousand turns of wire which will create the high voltage needed to fire the spark plug. The pulse transformer primary gets its current flow from the capacitor rather than directly from the flywheel magnet as in the flywheel magneto.

ELECTRONIC IGNITION

The solid-state electronic ignition is available on small gas engines. A battery is not necessary to operate the solid-state ignition because it is self-energized by the flywheel magnet as is the conventional magneto ignition system. The breaker points have been replaced with an electronic switch (SCR) which is triggered by a small coil. With this system, the only moving part is the flywheel magnet which does not actually make moving contact with other parts.

CHARGING THE CAPACITOR

As the flywheel magnet passes the input coil alternating current is induced in the coil. The diode, which is a one-way electrical cheek valve, allows the current to flow in only one direction. The flow charges the capacitor as the SCR is still turned OFF. The charge placed on the capacitor is trapped there by the diode since it is a one-way device and will not allow the current to flow back to the input coil,

TURNING THE SCR ON

After the flywheel magnet passes the input coil charging the capacitor, it then passes a small trigger coil which produces enough voltage to trigger (turn on) the SCR. A resistor is necessary to prevent excessive current flow which would damage the SCR.

DISCHARGING THE CAPACITOR

When the trigger coil turns on the SCR, it opens a path for the capacitor, which was left holding a charge, to discharge through the primary of the pulse transformer to the engine ground, This sudden burst or pulse of current through the primary winding of the puise transformer sets up a magnetic field which induces a very high voltage in the secondary winding to fire the spark plug. The action of the primary and secondary winding in the pulse transformer is similiar to that of the conventional coil. Spark timing is determined by the placement of the trigger coil.

TIMING ADVANCE

Two trigger coils could be used to trigger the SCR. The first trigger coil would be connected to the SCR through a high value resistor which would allow this coil to fire the SCR only at high speed. The other trigger coil placed after the first would fire the SCR at low speed.

With this arrangement, the SCR would not be fired until near TDC at low speed. When the engine speed increases to the point at which the first trigger coil produces enough voltage to overcome the higher resistance in its circuit, the SCR would be fired earlier causing earlier firing of the spark plug

WHY ADVANCE TIMING

From the instant the spark plug fires until the burning gas mixture expands to create maximum push against the piston takes time. The time needed to "build the fire and get it going" is nearly the same at all engine speeds.

At idle speed only a few degrees of crankshaft rotation are needed to provide this time. As the crankshaft turns faster, the spark plug must fire earlier in order to provide the same amount of time to get the fuel mixture burning. This is called timing advance.

CARBURETION

The carburetor controls the engine speed and provides it with a correct air-fuel mixture. The problem of providing a correct air-fuel mixture is complicated by the fact that the carburetor must provide this mixture through a wide range of engine speeds, varying loads, and varying temperatures. A carburetor which can do all of these things is complicated and expensive. On small gas engines, carburetors are designed to do as many of these things as possible while keeping the carburetor simple and inexpensive.

On four-stroke cycle engines, when the piston moves downward on the intake siroke, the intake valve is held open. Air rushes through the carburetor to fill the space being created by the moving piston. The moving piston is creating a partial vacuum above it. In this sense the engine is an air pump thai pumps in large amounts of air on the intake stroke and emits large amounts of hot air and exhaust gas during the exhaust stroke.

SPEED CONTROL

The engine speed is controlled by a flat disc called the throttle butterfly which restricts the How of air through the carburetor and controls the air-fuel mixture to the engine. Note that unless the throttle butterfly is wide open the engine cannot get all the air it wants. This restriction by the throttle causes a partial vacuum to be created behind it.JThis is referred to as the intake vacuum. 

When the engine is running smoothly at low speed and under no load, the intake vacuum will be quite high for the throttle is restricting air flow to the engine. Opening the throttle will allow more of the air-fuel mixture to the engine and the speed will increase. 

An engine which is pulling hard will have the throttle opm wide in proportion to the engine speed and the intake vacuum will be low. When an engine is under a light load, the intake vacuum will be high for the throttle will be limiting the air flow to the engine and the engine speed will be controlled.

THE CHOKE

The choke is a restriction in the outer end of the carburetor to provide an extra rich air-fuel mixture for starting. When the engine is cold, the fuel will not vaporize properly and an additional amount of fuel is needed to start the engine. The choke may be either a sliding tube or butterfly. 

It creates a restriction that cuts down the air flow to the engine and causes additional fuel to be drawn into the air stream. Some engines utilize a small primer pump instead of a choke. The primer pump injects a small amount of extra fuel into the air stream to create the rich mixture needed for starting.

CAUTION

Do not attempt to choke engines by putting the hand over the carburetor inlet. A misfire (backfire) could cause serious burns. Never look directly into the carburetor while the engine is being cranked.

AIR-FUEL MIXTURE

Good combustion requires a correct air-fuet mixture, A correct air-fuel mixture is one that has enough air to completely burn all the fuel. A mixture that has too much fuel is called a rich mixture. An engine running on a rich mixture will have reduced power and will emit black smoke from the exhaust pipe. Running an engine with a rich air-fuel mixture will result in rapid build up of carbon on the piston, valves, and head.

A mixture that does not have enough fuel for the air entering the engine is called a lean mixture. A lean mixture results in severe loss, of power and a tendency for the engine to "surge" (speed up and slow down constantly). If the engine is operated on a lean fuel mixture under load, overheating wilt result which can lead to a breakdown of the lubrication on the cylinder walls and allows the rings to scrape the cylinder walls and may cause them to seize (freeze up).

THE VENTURI

As. air rushes through a restriction, it must speed up. The increased speed of the air through the restriction causes a low-pressure area in the restriction. A restriction is placed in the carburetor air horn to cause a low-pressure area. This restriction is called the VENTURI.

A tube is connected from the fuel bowl into the venturi so that as air passes through the venturi, fuel is drawn into the air stream by the low pressure just as Coke is drawn through a straw. Creating a low pressure in your mouth causes the Coke to be drawn into your mouth. When the throttle is opened wider, the air flow will increase and the pressure in the venturi will become even lower, increasing the fuel flow into the air-stream, The amount of fuel drawn out of the fuel bowl is determined by the amount of air flowing through the venturi.

The mixture is consistent over a wide range of speeds. Opening the throttle wider will allow more air through the carburetor. This additional air will cause more vacuum in the venturi which will draw additional fuel into the airstream. The proportion of air to fuel will be the same, providing enough air to properly burn the fuel allowed into the cylinder.

Also, mixing fuel with the air in the venturi helps to turn the fuel into a vapor mist rather than drops of fuel. Fuel that reaches the cylinder in droplet form witl not burn properly. Only fuel that is changed into a vapor will burn properly in the engine. A rich fuel mixture allows drops of fuel into the engine. Instead of burning quickly like the vapor, the fuel drops tend to "wash" the oil film from the cylinder wall and cause undue wear on the rings and cylinder wall.

THE HIGH-SPEED AND INTERMEDIATE-SPEED CIRCUIT

The high-speed or load circuit is the real heart of the carburetor for fuel economy, engine power, engine temperature, and engine life are all dependent on the correct mixture during normal speed and load operation. The illustration at the left shows the major components of the circuit during normal operating conditions. The throttle butterfly is regulating the air How into the engine. The venturi is creating a low-pressure area to draw the fuel from the fuel bowl.

The carburetor shown here utilizes a float to maintain a constant fuel level. Some carburetors use other methods to maintain a constant fuel level. The fuel level is very important. An increase of as little as one-sixteenth inch in the fuel level will make the fuel easier to pull into the airstream in the venturi and will cause a rich mixture. A low level will cause a lean air-fuel mixture.

The nozzle is a precision tube which usually is removable. It provides the seat for the needle valve and extends into the veiituri as shown here. The nozzle is made of brass or other soft material and is subject to wear and damage from abuse.

The fuel metering adjustment needle valve adjusts the flow of fuel into the nozzle. It limits the amount of fuel that will be drawn into the airstreatn flowing through the venturi. This adjustment is made with the engine warm and running at least at half speed. Never operate engines at high speed when the engine is not under load! The engine may reach a speed at which mechanical failure can occur in the connecting rod or other fast-moving parts.

Notice the idle bleed hole located in a flat ring turned in the threaded portion of the nozzle. This allows fuel to enter the idle circuit (see idle circuit) on this type carburetor. On some older models this area of the threads was not turned flat but was threaded all the way up. On these models the old nozzle cannot be replaced in the carburetor because the idle bleed hole will not align with the matching hole in the carburetor.

If these holes do not align, there will be a loss of the idle circuit and the engine will die when the throttle is returned to the low speed position. Once the nozzle has been moved for any reason, it should be completely removed. If it does not have a flat area completely around the nozzle in the thread area, it must be replaced with a new nozzle.

THE IDLE CIRCUIT

The idle circuit is necessary to supply a correct air-fuel mixture to the engine when the engine is at idle and low speeds- Air flow through the venturi at low speeds is too slow to create the low-pressure area needed to draw the fuel into the venturi. A low-pressure area (vacuum) exists behind the throttle butterfly during idle since the throttle is. restricting the air flow into the engine. A separate idle circuit connected behind the throttle comes into operation when a high vacuum exists behind the throttle.

Gas is drawn by the low pressure behind the throttle butterfly from the fuel bowl past the idle mixture screw. Air is also drawn into the idle circuit through the air bleed in the air horn near the venturi. Some air is also entering the engine around the throttle butterfly. This air has no fuel since it passed through the venturi too slowly to draw fuel from the fuel bowl.

This air entering around the throttle and the air carrying a rich mixture of fuel is entering through the idle mixture needle valve. Adjusting the idle mixture screw limits the amount of air fuel entering from the idle circuit which mixes with the air entering around the throttle butterfly. This adjustment is made only with the engine at operating temperature and at the correct idle speed (see Basic Carburetor Adjustments).

Some carburetors utilize the fuel discharge holes in the venturi for air bleed during idle (see the illustration at the bottom of the opposite page). During high-speed operation the low pressure in the venturi draws fuel through the high-speed fuel needle valve and through the fuel discharge holes in the tube extending through the venturi. When the throttle is closed and the vacuum is greater behind the throttle butterfly than in the venturi, air enters through the fuel discharge holes on its way through the idle circuit.

Note that during idle the fuel also comes through the high-speed needle valve. The adjustment of high-speed needle valve can also affect the idle mixture. Always adjust the high-speed mixture first and remember that anytime the high-speed mixture is changed, the idle mixture should be readjusted.

CARBURETOR FUEL SUPPLY

A constant fuel level below the venturi is necessary to maintain a stable air-fuel mixture. Slight differences in the fuel level in the carburetor float bowl will affect engine power and performance. The fuel level can be controlled in a number of ways. A few of the more common techniques will be discussed here.

THE FLOAT

A common method of controlling the fuel level is by using a float and needle valve. With no fuel in the float bowl of the carburetor, the float is lowered leaving the needle valve open. The fuel will flow from the tank into the float bowl and will raise the float. When the fuel reaches the level determined by the float setting, the needle vaive closes against the seat and stops the fuel flow.

As fuel is drawn out of the fuel bowl, the float drops slightly, allowing the needle valve to admit more fuel. The fuel level is very accurately maintained by this method. Float type carburetors are limited to near level operation. They are more expensive to build and repair, and they require very precise adjustment.

THE DIAPHRAGM CARBURETOR

This carburetor uses a light flexible diaphragm to open the needle valve to admit fuel. The diaphragm holds the needle valve open to admit fuel. The fuel enters the bowl and pushes against the diaphragm allowing the light spring to close the valve. Thus, a constant amount of fuel is maintained by the diaphragm. This carburetor can be used on engines that must be tilted during operation, for example, outboards and chain saws. Sometimes engine vacuum is utilized in aiding the control of the diaphragm.

SUCTION FEED

The suction feed carburetor uses a shallow fuel tank mounted directly below the venturi section of the carburetor. The shallow fuel tank replaces the float bowl. Since the tank is shallow, the difference between the fuel level in a full tank and a near empty tank will not create excessive differences in the fuel mixture. It does tend to provide a rich mixture when the fuel tank is full and a lean mixture when the tank is nearly empty, it is therefore necessary to have the tank half-full when adjusting the carburetor.

This carburetor may not have an idle mixture adjusting screw. The idle mixture will be dependent on the high-speed mixture. This carburetor is simple and maintenance free. It requires a clean air cleaner, clean fuel, and a tight connection to the engine.

The fuel pipe has a fine mesh inlet screen and may have a check ball. If fuel has been allowed to remain in the engine during storage or if dirt has gotten into the tank, the screen and check ball may become clogged. Remove and clean thoroughly. If the fuel tube is brass, it is a press fit in the carburetor body. To remove a brass fuel tube, clamp the tube lightly in a vise and pull the carburetor off. If the tube is nylon, it is threaded into the carburetor body and is removed with a socket wrench.

BUILT-IN FUEL PUMP

A fuel pump built into the carburetor may be utilized to maintain a constant fuel level which eliminates the need for the float. On single cylinder, four-stroke cycle engines there is a partial vacuum just behind the throttle plate on the intake stroke since the pis ten is moving downward and the throttle is restricting the air flow.

During the other three strokes the intake area is at normal pressure. This creates a pulsing vacuum in the intake area between the intake valve and the throttle. A flexible diaphragm placed in this area is pulled in by the intake vacuum during the intake stroke and is released during the compression, power, and exhaust strokes. The flexible diaphragm will be moving back and forth. The other side of this pulsating diaphragm can then be used as a fuel pump to draw gas from a large fuel tank up into a small inner tank.

Flapper type check valves cut into the diaphragm direct the fuel through the pump into the inner tank. The fuel pump can pump fuel faster than the engine can use it. The excess fuel is allowed to overflow back into the large fuel tank, thus maintaining;! constant fuel level in the small inner tank without using a float.

The air flow through the venturi causes a partial vacuum which draws the fuel from the inner tank just as it does from the float bowl on the float type carburetor.

Many of these models also have the magneto stop switch on the carburetor speed control. When removing or servicing this carburetor, care should be taken to note the location of the wire coming from the magneto. If this wire comes in contact with the engine ground, the magneto will be disabled.

Diaphragm failure may be the cause of hard starting or may lead to an excessively rich fuel mixture if the diaphragm ruptures. A hole in the diaphragm would allow fuel to be pulled from the fuel pump directly into the intake manifold. Diaphragm replacement is simple, but care must be taken to get the diaphragm placed correctly in the fuel pump.

ENGINE SPEED CONTROLS

Engine speed is controlled by the operator's manual speed control and the governor. Most small gasoline engines which are used to power a constant load such as a mower or tiller must employ a governor to maintain a nearly constant speed as the load changes. Changing or removing the linkages on lawn mowers usually results in the loss of the governor as a speed control. The engine speed is then nearly uncontrollable.

The engine will act as though it has almost no power and it will slow down excessively upon encountering a load. The operator must then increase the engine speed w<th the manual speed control lever. Once the load is reduced, the engine will overspeed. A normally functioning governor is essential for satisfactory operation on machines such as mowers, tillers, and generators.

AIR VANE GOVERNORS

The air vane governor is a simple and inexpensive device for controlling engine speed. An air vane located under the shrouding near the flywheel senses the engine speed by the amount of wind created by the fins of the spinning flywheel. As the engine speed increases, the increased force of the air flow created by the flywheel will push against the air vane.

The air vane is connected by a wire linkage to the throttle control arm. It pulls against the governor spring to close the throttle thereby reducing the engine speed- The speed of the engine is determined by a balance between the pull created by the air vane and the pull on the governor spring from the hand control.

If the operator moves the hand control to increase the engine speed, the governor spring will pull harder on the throttle control arm opening the throttle wider. The engine speed will increase until the air flow from the flywheel against the air vane increases to equal the pull of the governor spring.

If the engine encounters an increase in load, the engine speed begins to decrease and the air flow against the air vane will decrease allowing the governor spring to pull the throttle open wider to retain the engine speed. The governor will maintain constant speed as conditions vary.

MECHANICAL GOVERNORS

Mechanical governors are considered to be somewhat more precise and dependable than air vane governors. They are more expensive and add weight to the engine. The mechanical governor senses the engine speed by the amount of centrifugal force exerted on rotating weights located inside the crankcase. The type shown in the illustration has weights mounted on a pivot so that as the weights are thrown outward by centrifugal force tbf; center pin is lifted upward.

As the engine speed increases, the weights are spinning faster and the force exerted by the weights to the center pin is increased. This acts to slow the engine down. Again, as with the air vane governor, the engine speed is determined by the balance of force created on the governor spring by the hand speed control and the force produced by the spinning weights.

If a load causes a reduction in the engine speed, the centrifugal force acting on the spinning weights will be reduced allowing the governor spring to open the throttle to increase the engine speed. As the engine speed recovers, the governor will again exert pull against the governor spring to maintain the engine speed.

FUEL SYSTEM SERVICE

Many of the problems commonly associated with the fuel system may actually he electrical problems such as a had spark plug or a weak spark caused by a bad condenser or breaker points. Even a rusted magneto armature may cause symptoms similar to fuel problems. Check the condition of the spark plug; (see Spark Plug Service) and the quality of the spark before blaming the fuel system for failure to start or for poor performance. If the spark plug condition is good and if a strong spark is present, the following suggestions may help find the problem.

ENG1NE FAILS TO START

Check Fuel Tank, Make certain that there is sufficient fuel. Make certain that the fuel is fresh. Stale gasoline can cause hard starting and poor performance. Check the fuel tank for dirt or grass, etc. Mowers and tillers tend to collect foreign matter in the fuel tank. Remove the tank and clean it completely tf foreign matter is present. It is good practice to wipe off the top of the fuel tank before removing the filler cap.

Check the Choke. On many small gasoline engines the choke is operated automatically by the hand speed control lever. Improper adjustment of the speed control cable may be causing the choke to close completely. If necessary, remove the air cleaner to determine if the choke is closing completely.

Remove the Spark Plug, After cranking the engine several times with the choke fully closed, remove the spark piug and observe the condition of the plug (see Spark Plug Service).

ENGINE STARTS BUT SURGES INSTEAD OF RUNNING SMOOTHLY

Incorrect Fuel Mixture. Adjust the carburetor (see Carburetor Adjustment Section). Surging usually indicates a lean fuel mixture unless accompanied by black smoke from the exhaust pipe.

Incorrect Governor Operation. Incorrect connection of governor linkages, bent or broken linkages, incorrect linkages, or binding or rubbing of the linkages can cause incorrect governor operation. Check these linkages tor free operation. On mechanical governors, cVck for correct adjustment.

Air Leaks. Air leaks into the carburetor can occur at the gasket where the carburetor attaches to the engine. Most carburetors are held on by two cap-screws which are readily loosened by vibrations allowing air to enter past the gasket. Do not overtighten these capscrews for they are easily stripped in the aluminum engine block.

Also check the throttle shaft for air leaks, ff the throttle shaft is loose in its bushings, air will enter around the throttle shaft and will cause the fuel mixture and the engine speed to change as the throttle shaft moves around in the bushing. This condition usually calls for replacement of the carburetor body.

CARBURETOR SERVICE

In most cases it will be necessary to remove the carburetor if disassembly is required. The first step is to draw a diagram of the speed control linkages and springs because the proper operation depends on the correct connection of these linkages. If these linkages are already disconnected or missing, it will be necessary to consult the manufacturer's literature or find a similar engine to determine the correct connection.

Do not bend the linkages when removing them from the carburetor. Bending the linkages will change the length and affect governor operation. Remove the bolts that hold the carburetor to the engine and twist the carburetor assembly to disconnect the linkage. Needle nose pliers are helpful in removing springs. Be very careful not to stretch the springs.

An assortment of good screwdrivers, pliers, and a clean, well-lighted work area can be very helpful for carburetor disassembly, cleaning, and reassembly. Oean the exterior of the carburetor with a stiff brush and cleaning solution before disassembly. If the carburetor is to be disassembled, it is usually worth-white to rebuild the carburetor.

A kit of necessary parts can be purchased that contains the parts that normally wear and cause trouble, for example, gaskets, needle valves, and seats. Check the kit to determine the parts which are provided before disassembly to determine which parts should be removed.

After disassembly, the carburetor should be soaked for a few minutes in carburetor cleaner to remove the gum and varnish residue. Caution: Carburetor cleaner is extremely painful if it is brought in contact with the eyes or skin. Avoid contact with the cleaner.

Wash the parts in water thoroughly after cleaning them with carburetor cleaner. Do not attempt to brush or blow out the carburetor passages until they are thoroughly washed out with water. Remove all gaskets and plastic parts. Do not place them in the carburetor cleaner for some of them will be dissolved by the cleaner.

Remove and replace needle valves and seats very carefully. They are made of soft material und can be very easily damaged. Use only screwdrivers that are flat across ths tip and are the correct width for the screw. Use wrenches instead of pliers to remove fuel lines and hexagon head capscrews. When removing needle valve seats that are recessed, use a screwdriver that is wide enough to make good contact with the seat but not so wide that it will damage the threads on the sides. Usually j nontaper screwdriver is required.

Check the float for leaks. If a hollow brass float is used, leaks will allow fuel to fill the float. Shake the float near your ear to determine if there is fuel in the float,

Before replacing the needle valve seats and the needle valves, visually inspect the fuel passages to make sure that they are clean. Reassemble the carburetor with care. Remember to reconnect the linkages and magneto stop wire (if so equipped) before attaching the carburetor.

AIR CLEANER SERVICE

Smalt gasoline engines are often exposed to very dirty working conditions. A good, clean air filter is essential to efficient operation and long life. Remember that the engine is really quite an efficient air pump. An engine with a displacement of eight cubic inches will try to draw in eight cubic inches of air on each intake stroke. You can readily see that an engine running at full throttle will consume a great deal of air.

An air cleaner must be kept in good condition to admit that much air without allowing dirt into the engine. If the air filter starts to become clogged with dirt, grass, or other matter, it will restrict the flow of air through the carburetor. This is exactly what the choke does. A dirty air clearer will choke the engine, causing it to run on a rich air-fuel mixture which wiii cause toss of power, spark plug fouling, and carbon buildup.

The excess gas will tend to "wash down" the oil film from the cylinder walls causing improper ring lubrication and will lead to excessive wear or possibly engine lock up. Also, the excess fuel in the mixture will get past the rings into the crank-case, diluting the oil.

DRY PAPER TYPE FILTER

This type of air filter utilizes porous paper to allow air flow and collect dirt and foreign matter. Tap the filter element to jar the dirt loose, Blow dirt away by blowing from inside out with low pressure air. A vacuum cleaner is effective for cleaning this filter. If the filter still appears clogged, replacement is necessary. Do not attempt to soak or wash the dry paper element.

POLYURETHENE ELEMENTS

Air filters of this type can usually be cleaned several times. Clean the filter thoroughly with soap and warm water. Squeeze out and add a few drops of light oil before replacing. Make sure that the filter fits back into the metal holder and is retained so that it cannot be drawn into the engine.

OIL BATH AIR CLEANERS

Oil bath air cleaners are usually used on engines that are used regularly in dirty conditions. This air cleaner is capable of collecting larger amounts of dirt and is easily serviced. The incoming air travels downward toward the oil at a high rate of speed. The air is forced to make a sharp turn just above the oil. Dirt and foreign matter tend to travel straight into the oil and stick there. Most of the dust and dirt entering the air cleaner will collect in the oil.

The air then travels upward through a filter element before entering the engine. Check this element and wash it out if necessary. If the oil is changed regularly, the air cleaner will do a very efficient job of protecting the engine from dirt. The interval for oil change is determined by the amount of use and the operating conditions. Usually, instructions are labeled on the air cleaner.

SMALL GAS ENGINE STORAGE

The successful operation of a small gas engine depends on the care given it. A few precautions taken before storing an engine can prevent several problems which can occur during storage.

REMOVE ALL FUEL

Fuel that evaporates from an engine leaves gummy deposits that can cause serious problems. Drain the fuel tank and clean the filter screen. Drain the carburetor. On some models this can be done by pushing the small drain on the bottom of the carburetor fuel bowl. An excellent way to drain the fuel system is to run the engine until the fuel is used up. This also warms up the engine so that the oil change will remove most of the dirt accumulated in the crankcase.

CLEAN THE ENGINE

If necessary, remove air shrouds to clean around the cooling fins, governor linkage, and spark plug. Always replace the air shrouds for they are an essentia! part of the cooling system.

LUBRICATE THE CYLINDER WALL

Remove the spark plug (see Spark Plug Service). Add approximately one ounce of SAB 30 motor oil to the cylinder. Make sure that the piston is near top dead center before adding oil, especially on two-stroke cycle engines. Crank the engine several times to distribute the oil all over the cylinder wall area, valves, and valve guides. Replace the spark plug with a new plug (see Spark Plug Service).

REMOVE THE BATTERY

if a unit is battery equipped, the battery should be removed during storage. Care should be taken to record the battery's position and cable connections. If the battery cables are connected backward, the alternator diodes will be blown instantly.

Place the battery in a cool, dry place where it will not freeze. Hie battery should be fully charged when it is placed in storage and it should be recharged occasionally to maintain full charge (see Battery Section). Do not store battery on concrete. Place a small board under the battery during storage 10 keep it off the concrete.

RESTARTING AFTER STORAGE

1. Check oil level,

2. Clean air filter.

3. Check battery electrolyte level (see Battery Service).

4. Add clean, fresh fuel.

5. Adjust carburetor.

Adapted from:

SMALL GAS ENGINES

James A. Gray and Richard W. Barrow

School of Technology Indiana State Univetsitv

Prentice-Hall, Inc., Englewood Cliffs, New Jersey

© 1976 by Prentice-Hall, Inc. Englewood Cliffs, New Jersey

All rights reserved. No pari of this book may be reproduced in any form or by any means without permission in writing from the publisher.

Drawings by Robert F. MacFarlane