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Small Gas Engine Repair Page

If you are looking for information to fix your small engine, you have come to the right place. The following article has all the information needed to determine the problem. This page contains easy ways to determine why gas engines will not start, or will not run properly.

A gasoline engine needs the following three essentials to "run"
Fuel - Spark - Compression

There Is A Quick, Easy Test For All Three Essentials

Trouble Shooting

Spark- A quick test is as follows; place the engine out of bright sunlight, remove the spark plug, reconnect the ignition wire to the spark plug and lie it on top of the engine head, or metal of the engine. Give the rope a tug and observe if there is a good spark jumping the spark plug electrode? ( a good blue spark is ideal; this is a simple way to test sparkplugs) If not, try changing the spark plug and try again. If there is no spark you have an electrical problem, if there is a spark then the problem is either fuel or compression. A weak spark may not ignite the fuel-air under compression. Note the following colors and sound to the spark

Fat blue spark that cracks audibly indicates all is well
White spindly sparks indicates a problem in the spark producing mechanism
Reddish sparks usually indicate burnt points or a failing condenser.

The spark plug provides a path within the combustion chamber to provide a gap for the spark to jump which ignites the fuel air mixture.
Spark plugs have many heat ranges. The manufacturer of each engines decides which heat range is best, to provide the optimum operation for each engine type. The heat range of a new engine is usually on the cooler side of the available heat ranges. The proper range will keep the spark plug clean of carbon and other components of combustion.
As an engine wears and the compression drops and oil rings wear, the spark plug will not be hot enough to deal with the different gases and burnt oil caused by oil leaking past the oil rings of the piston. A spark plug of a greater heat value will help deal with these problems.
Each spark plug has a certain size thread and threaded area. Too short and the spark plug does not reach far enough into the combustion chamber, resulting in poor starts and poor combustion which results in less power produced. If the thread is too long the spark plug gap will reach too far into the combustion and will not leave enough room in the combustion chamber for the piston to travel. The piston will strike the end of the spark plug, damaging both the spark plug and top of the piston. It is important to choice the right spark plug for each individual engine.

Spark Plug Gap- Spark plug gaps are around thirty-thousands of an inch (.030). A quick comparison relating to thickness, is the dime which is about .050 of an inch. To remove the spark plug from the engine, turn counterclockwise.
To clean off heavy carbon particles, use a tiny screwdriver; scrape on and around the electrode and finish up with a small wire brush. When replacing the spark plug, be aware that you cannot tighten the spark plug as tight on an aluminum head as you can on a cast iron head. If you over-tighten, you could stripe the threads (there are various epoxy type solutions to repair stripped threads). Spark plugs can last a long time, as long as the engine is in good shape. When the engine starts to wear, the spark plug will carbon up, because of the excess oil burning in the cylinder and therefore it will need to be cleaned more often, or replaced. Spark plugs are not too expensive and it is worth replacing every couple of years, as this will help to insure easy starts and cleaner running.

Fuel- Smell it, it should not smell old and stale; thick and deeper yellow (old fuel loses the ability to vaporize). Gasoline left in the fuel tank over the winter can become stale and not support combustion. Stale fuel can cause a stuck check-ball; Fresh fuel is in order but not the same stale gas that was sitting all winter in the gas can. Once you get the engine running, any not to old fuel, will probably be ok to use. Fuel left for a long time tends to vaporise out, leaving behinds a thicker, stale gasoline which will not support combustion. Remember, it is the vapor which supports combustion, not the raw wet gasoline. If the fuel is stored in a very warm location, the fuel becomes stale in a shorter period of time. The smaller the amount of fuel, the quicker it becomes stale. It is best to use up all the fuel in the same season and not store it until the next season.

Is the fuel able to reach the combustion chamber or is the fuel filter or carburetor plugged? A quick test is to remove the spark plug, pour a tiny bit of fresh gasoline directly into the cylinder. Replace the spark plug and give the rope a tug. If the motor starts and runs briefly, fuel is the problem. Take the proper precautions when handling gasoline, keep the container away from flame and sparks, keep the lid on the gasoline container when not in use, keep gasoline off skin. Use in well ventilated areas.
Note: There should not be any raw gas anywhere on the outside of the motor: that would indicate a leak somewhere and could result in a fire!

How a Primer Works
A primer is connected into the fuel line; it has a one way valve within it, becoming a small pump. When you press on the primer bulb, fuel is pumped from the fuel tank towards the carburetor forcing the older fuel within the carburetor back to the fuel tank. New fuel is delivered to the carburetor which has better qualities for evaporation and causes the engine to start better. Any crack and leaking fuel in the rubber bulb will allow air to enter the fuel line and prevent any fuel from reaching the carburetor. When changing a primer, take note, it has a one way valve, and must be placed in the right direction or it will not work. As the primer bulb rubber cracks or loses it elasticity it will evenually collapse and not spring outward and will have to be replaced.

Small engine timing
Most small engines, such as lawnmower engines have fixed timing at the factory, and are not adjustable. Small engines where the timing is adjustable, the spark run point is 11-20 degrees before TDC. If you put a thin piece of paper between the points and slowly rotate the cranshaft by hand, the point at which the paper just slips out is the TDC.

Compression
A quick test to test for compression is as follows; turn off the ignition and remove spark plug. Place your thumb over the spark plug hole and give the rope a tug. If there is no compression or low compression this would indicates internal problems such as valve, rings or piston failure. If you have access to a compression gauge, and get a reading of around 65-70 psi., that is good. Any compression reading below 45 psi., indicates a well worn engine.
Engines with very low compression are very hard to start and a very quick pull is required to get the compression up high enough to start the engine.

If the compression is low when you test with a compression guage, try adding 1-2 tablespoons of oil directly into the spark plug hole. Try cranking over and retest the compression. A rise in the compression indicates worn rings. No change indicates valves are not closing properly.

Reasons for poor compression can be, spark plug loose, cyclinder head bolts loose, cylinder head gasket leaking, carbon blocking exhaust valve from closing properly.

Re-bounce Compression Test
Another simple test for compression is the re-bounce compression test. Turn off the ignition switch, rotate the flywheel by hand in a counterclockwise direction (viewed from the flywheel side of the engine), feel the resistance as the piston reaches top dead center. As it approaches the top, quickly rotate the crankshaft against the resistance and you should feel a sharp re-bounce (bounce backward). This re-bounce indicates there is enough compression to run the engine.

Most four stroke engines have a normal compression of around 75 pounds per square inch. (psi). Two stoke engines are around 90 psi.

Weed Eater No Spark
The spark is produced each revolution of the crankshaft by passing a permanent magnet (embedded in the flywheel) past a coil of wire, when the magnets passes the coil of wire, a current is produced in the primary windings (fewer windings) of the coil and then the collapsing magnetic field of the primary windings cuts through the secondary windings (large amount of windings) this produces a very large voltage at the spark plug, jumping the gap and returning to ground of the engine, making a complete circuit.

. The spark mechanism in the weed eater is a very simple mechanism and everything has to be perfect to produce a spark. Over time rust and corrosion happen around the bolts that hold the spark mechanism in place. Try using a new spark plug first, before trying anything else, if this does not help; then disconnect the throttle cable, undue the five bolts that hold the weed eater together and separate the unit. Next unplug the wires to the stop switch.

Now with the unit on the bench you can take a few measurements with an ohm-meter. There is a primary and secondary wrap of wires within the spark mechanism; so you will get a high and a low resistant reading. The important factor is to get some form of reading, no reading would indicate the wire inside is broken and therefore the unit is defective. Even if you don't have experience with an ohm-meter, continue by removing the two hold down bolts and remove the spark unit. Use sand paper to clean the unit and bolts so you get a good contact between the spark unit and body of the engine. To re-assemble, Place the spark unit back on the motor and tighten down the two bolts slightly by hand, then place a business card or equivalent thickness piece of paper between the spark unit and flywheel, rotate the flywheel until the magnets attracts the spark unit. Tighten down the two holding bolts, then remove the paper, this provided the correct gap between the spark unit and flywheel.
This is also a good time to replace the starting rope. Don't remove the plate on the rope assembly as there is a wound up spring that can fly out and cause injury. Pull the start rope all the way out, then jam a nail of stiff wire alongside the unit to keep it from re-winding. If the rope is already broken, then wind up the spring mechanism by hand and jam in place. Remove the old cord, and fish in the new cord with a fine wire, attach it the same way the old cord had been. Remove the nail that is holding the unit from turning and allow it to wind in the new cord. Put the motor back together again and check for spark. To put the weed-eater back together, reconnect the shut off wires, turn the drive shaft, from the lower end of the drive shaft (where the line goes), by hand to line up the spine where the motor connects to the drive shaft. Slowly slip the unit together again. Place the five bolts back into place. Move the throttle wide open and jam in place with a nail etc. Place throttle cable back in place, remove nail. A good fast pull is required to produce a good healthy spark. Typically the primary coil will read 2-3 ohms and the secondary windings 8,000-10,000 ohms.

spark coil

Magneto System With Points
As the flywheel turns, a magnet in the flywheel sweeps past the magneto coil energizing the primary winding some 300 volt. This voltage flows through the closed points and engine ground to the coil. When the points open, the primary voltage collapses into the secondary winding producing 12,000 volts at the sparkplug

If you need to remove the carburetor on a weed eater, be advised that you will have to purchase the correct carburetor gaskets. If you dissemble the carburetor, you will need the exact gaskets, as it has built in reed valves as part of the gas delivery system. If the weed-eater is more than a couple years old the fuel line will also need replacing; the fuel line gets very brittle (from the heat of the engine) and will snap in two easily. I have on occasion found I could splice in a new fuel line near the fuel tank as the fuel line remains more flexible for a longer period of time, near the fuel tank.

Chainsaw Will Not Start
The most likely cause for not starting, is a fuel problem. So start here, remove the spark plug and pour in a little good clean gas (no oil mix), directly into the combustion chamber, replace the spark plug and spark wire and give a pull on the rope. If it starts, fuel delivery is your problem. If not, then do a spark test. To fix a fuel problem dump out the gas in the tank and "fish out the flexible fuel line with the attached fuel filter in the gas tank. Form a wire into a hook to do this. Usually you will find that the fuel line has cracked and is drawing in air instead of fuel, then replace it and the filter at the same time. If the fuel filter has become plugged up because of grime, then just replace the filter.
With chain saws it is easy to introduce dirt into fuel tank while filling in the field. Carry a small one inch paint brush and brush around the gas and chain oil fill plugs before removing; this will prevent grime from dropping into the tank when you remove the fill plug. Remove the carburetor cover after two or three tanks of gas and clean the air filter. Use the paint brush to do this. As the air filter becomes plugged up, less air is mixed with the gas and a very rich mixture is created which will wet out the spark plug causing it to short out, the result is the engine will not start. It’s the same principle as leaving the choke fully on. Older chainsaws will not idle on their own because of wear around the crankcase seals, allowing air to enter which changes the fuel mixture and pumping action of the carburetor.

Most chainsaws use two stroke engines because of their light weight and high power output. If a chainsaws is stored with gas left in the fuel tank, it can cause problems within the carburetor to the diaphragm and the fuel needle, which may stick, because the old fuel usually turns into a varnish like liquid. Old fuel diaphragms can dry, crack or tear. Build up of old varnished gas can plug up the low and high speed fuel jets.
The jets can usually be cleaned by using a small strand of copper wire, which you can carefully pass it through the fuel jet holes. Never use a hard material such as drill bits, the jets are soft metal and can be damaged. Primer bulbs sometimes collapse and will eventually crack stopping the flow of fuel. Replace them at the first sign of cracking. Compression of typical chainsaws should be around 120 psi.

Chainsaw Bars
Most chainsaw bars are reversible; and under normal home use, should be turned over once a year; this will even out the wear.
To check the tension of the cutting chain, using moderate force, slide the chain around the bar. Keep on mind a new chain will stretch a bit after 15 minutes of use. Recheck tension from time to time. Keep the bar lubricating oil topped up and front idle sproket well greased.

Chainsaw Chains
Brand new chains should be soaked in motor oil a few hours for a few hours before installing on chainsaw, but mostly they come well oiled. Run the saw a few minutes at half throttle and let the cutting chain turn freely. Then do some light duty cutting and recheck chain tension, the chain should be free enough to easily turn by hand.

Changing The Sprocket
To remove the sprocket lock nut, screw a plastic piston plug into the sparkplug hole to keep the crankshaft from turning. An alternate choice is to remove the sparkplug and stuff the combustion chamber with cotton clothesline. If you use air tools, there is enough quick blows to remove the nut without trapping the crankshaft.

Poor Power
If your chain saw has poor power, removing the muffler and clean out the carbon from the exhaust port (turn the engine over to get the piston below the exhaust port, so you don't damage the piston, while scaping out the port). Also check the air filter for dirt. When you remove the muffler, clean out all the oil packed sawdust in behind the muffles and in the cooling fins. 25% of the cooling comes from the cooling fins behind the muffler. If the engine overheats it will stop running and will not start until it cools down.

Checking Reed Valves
Remove the air cleaner and start the engine. Hold a piece of white paper next to the air intake port. Oil spots on the paper indicate the reed valve should be replaced. Reed valves should not bend away from the mounting plate more than .010 inch.

When a chainsaw starts and runs for a long while, then stops and can't be started, it is usually an overheating problem. If a chainsaw gets overheated the fuel starts boiling and this causes a vapor lock, stopping the delivery of fuel. In time dirt and grime plug up the fins around the cylinder and head, preventing the engine to cool properly. To fix this you must clean the outer engine parts, as it was when it was new, then it will run again, just like new. You must remove the muffler to get at the cooling fins on this side of the motor

CAUTION
If the chain becomes loose enough to "jump" off the bar, shut the chainsaw off immediately! I once saw the results of one fellow who thought if he "revved" up the saw; the chain would somehow jump back into the track. Unfortunately the chain flung back into his face and cut him up badly.

Two-Cycle, Why Oil Is Mixed With Gas
The reason oil is mixed in with the gas in two-cycle engines, is to provide lubrication to the moving parts, as there is no oil reservoir, nor any pump to move the oil to moving parts. The oil-gas mix enters the crankcase and lubricates the moving parts as it moves towards the combustion chamber.
The fuel-oil mixture has to be right to provide the proper combustion and proper lubrication. Too much oil and you will get a build-up of carbon, too little and you will have premature wear of the engine. If there is no oil in the fuel, the engine will seize up. You must also use an approved two-cycle oil which burns cleaner than regular car oil.

If you fill the tank of a two-cycle with regular gas by mistake; just remove the fuel and fill with the proper oil-gas mix. No harm, is done, even if you have already run the engine for a short period of time (the oil deposited in the crankcase will protect it for a short while). If you fill the tank of a four-cycle lawnmower with gas mixed with oil for a two-cycle engine, it wouldn't harm the engine even if you run it a short time. Drain it out and replace with clean unmixed fuel.

Small Engine Runs A Short Time And Quits
When a small engine will only run a short time and quits, it probably starves itself of fuel. The most common problem is that the fuel cap vent has become plugged or damaged and no air can enter the fuel tank. As an engine runs. air must replace the fuel, as it is drawn into the carburetor or a vacuum is created and eventually the engine can no longer draw fuel. Check the fuel cap.
Also if the cooling fins on the cylinder and head are not cleaned out regularly, they can become plugged-up with dirt and grass etc. causing the motor to overheat and quit. On a very hot day, the engine just may not be able to cool itself properley and overheat. Just let it sit in the shade for awhile and cool down before re-starting.

Stalls While Idling
Other causes for not idling; are, dirty air cleaner, plugged airvent in fuel tank cap, water in fuel, dirty or incorrectly gapped sparkplug, leaking reed valve on 2-cycle engines, air leak at base of carburetor, dirty fuel mixture needle or incorrect adjustment.

Adjusting Idle Mixture - 2 and 4 cycle
Warm the engine to operating temperature. Make sure choke is in the off position and air filter is in place. Approximate starting adjustment is 1 1/2 turn out. While running the engine at idle speed slowly turn the idle adjustment screw in until the engine starts to miss or slow down, back out slowly until engine runs smoothly, then back out 1/8 more turn.

Reasons Engine Will Not Idle
Plugged air cleaner
Leaky carburetor gasket
Throttle of choke shaft worn
Air- bleed restricted
Damaged diaphragm
Stuck or dirty ball-check
Fuel pick-up restricted
Idle port restricted
Damaged idle adjustment needle
Fuel inlet plugged

Adjusting High Speed Mixture - 2 and 4 cycle
If the engine has a high speed adjustment screw, warm the engine to operating temperature. Make sure the choke is in the off position and air filter is in place. Approximate starting adjustment is 2 turn out. Run the engine at high operating speed and back out the high mixture screw until the engine starts to slow down, note the position of the mixture screw, then slowly turn in the high speed mixture until the engine starts to slow down. Note the position of the high speed mixture screw. Adjust the high speed mixture between the two extremes.

Removing Carburetors And Cleaning
Most small engines carburetors have two bolts holding it onto the engine. To remove, drain the fuel out of the fuel tank. Another option is to remove the fuel line from the carburetor and jam a tapered piece of wood or bolt into the end of the fuel line. Remove the air- cleaner, remove the carburetor hold down bolts and linkage. Take note of the linkage setting as there may be more than the one setting (to mark, use a felt marker pen). Wash down the carburetor with some kerosene or varsol, using an old paint brush. Take care not to get any into your eyes. Place the carburetor on a clean piece of cloth and remove the four bolts holding it together. Use a short (12-16 inch) piece of clean plastic gasoline tubing; Place over the small fuel delivery channels and blow on the other end with your mouth, which will blow out anything blocking the flow of fuel. To re-assemble, you will have to buy or make new gaskets. Stores like Canadian Tire or Auto parts stores handle this do it yourself product. A leather hand-punch can be used to make the holes in the gasket material. Place the carburetor back onto the engine in the reverse order that you removed it. Take note that two-cycle carburetors require a special material gasket that have to be purchased for each exact carburetor; it also acts as valves for the pumping of fuel.
Generally most carburetors can be cleaned on the engine by removing the needle valve (mixture adjusting screw), lock nut and o-ring. Apply compressed air to the needle valve opening. Monofilament can also be used to clear out carburetor passages.

Lawnmower Backfiring
Your lawnmower backfires and will not start; if his happened after you pushed the lawnmower over a large rock or solid object, chances are the key in the keyway between the flywheel and crankcase sheared off and now the timing is no longer correct. To fix this you will have to remove the flywheel and place a new key in the keyway.
Also running the engine over lean can cause carburetor spit-back on sudden acceleration.
Other backfiring problems such as out through the muffler or carburetor, may be caused by extreme carbon build-up on the valves and valve-stem guides, which prevents the valves from closing fast enough and far enough. The valves will not be able to contain the exploding fuel. This usually happens because the oil is hardly ever changed, it loses its lubricating qualities, becomes full of carbon causing harmful carbon deposits on the valves and guides. Heavy carbon deposits on the piston head causes "dieseling"( the engine keeps running a short while after it is shut down) because the carbon becomes red hot and ignites the fuel-air mixture even though there is no spark present. There are fuel additives available which can help remove carbon and grime within the engine.

Other reasons for backfiring are, dirty air cleaner, choke stuck closed, caburetor flooded, carburetor mixtures incorrect, dirty carburetor, exhaust valve sticking, incorrect ignition timing - if adjustable.

Lawnmower Engine Misfiring
Misfiring is when the fuel-air mixture is not ignited. The most common reason is a bad spark plug. Too rich or too lean a mixture can also cause a misfire. Sticking valves or poor valve sealing also cause misfiring.

Engine Surging
Engine surging is when an engine alternates between running fast and slow at the same throttle setting. The most common reason is a partially plugged fuel tank vent. A dirty air filter can also cause this problem.

Other reasons for surging are, fuel restricted to carburetor, throttle linkage or butterfly binding or sticking, carburetor mixtures incorrect, carburetor float level to low and speed governor sticking or binding.

Stalls On Acceleration
Reasons may be dirty air cleaner, dirty fuel filter, incorrect fuel mixture settings or damaged fuel mixture needles.

Lacks Power
Reasons may be, dirty air cleaner, loose spark plug or spark plug ignition wire, low oil level, dirty spark plug or incorrectly gapped, choke partially closed, carburetor mixture incorrect, carbon blocking muffler or exhaust port, ignition timing incorrect - where adjustable, oil seals leaking on 2-cycle engines.

Reasons For Engine Knocks
Equipment loose or improperly adjusted
Excessive carbon in combustion chamber
Loose flywheel key or flywheel nut
Overly advanced ignition timing
Loose or worn connecting rod
Worn cylinder
Broken piston skirt
Broken piston ring

Reasons For Hard Starting
Plugged air filter
Throttle or choke shaft worn
Choke not functioning properly
Air- bleed restricted
Damaged diaphragm
Diaphragm upside down
Plugged fuel tank filter or vent
Fuel pick-up restricted
Damaged adjustment needles
Main nozzle restricted
Dirty, stuck float needle and seat
Fuel inlet plugged

Some engines use a soft key on the flywheel and can have a partially sheared key from hitting something. This can cause the timing to be off and cause hard starting.

Removing Flywheel
To get at the points and condenser you have to remove the flywheel. Do not hit the flywheel with a hammer; you will damage the flywheel or other parts of the engine. Hitting the flywheel with a hammer will reduce the Strength of the permanent magnet embedded in the flywheel and will cause reduced spark. Do not try prying it off with a screwdriver, as you will probably crack the engine casing and warp the flywheel. Use a proper puller designed for the job which will pull it off with proper balanced forces. To remove the nut holding the flywheel in place, use an air or electrical driven impact tool and turn the flywheel nut in the opposite direction of crankshaft rotation. Do not try jamming a screwdriver into the air fan blades to keep the engine from turning over and attempt to use a wrench; you will only end up breaking some blades off the fan blades.

OK for the rest of us who don't own any impact tools, try this; place a few drops of penetrating oil on the threads, then take a boxed end wrench and rotate the crankshaft until you can feel the compression taking place. While holding the wrench in this position, give the outer end of the wrench a whack with a hammer. The compression may hold the crankshaft just enough to dislodge the nut. An alternate way is to remove the sparkplug and stuff cotton clothesline inside the combustion chamber; this will prevent the crankshaft from rotating.

Reasons For Overheating Engines
Excessive engine loading, especially on very hot days
low oil level or wrong viscosity oil
Cooling air flow obstructed or clogged cooling fins
Lean air-fuel mixture
Ignition timing incorrect
Carbon in the combustion chamber
Running the engine at too high a revolution for a prolonged time

How To Remove Carbon From The Combustion Chamber
Try using a fuel additive to help remove carbon first; if this doesn't work, then go the manual route to removing carbon. Remove the cylinder head gasket
Rotate crankshaft so piston is top dead center, scrape away carbon with a scraper (small putty knife) and brush away carbon with a wire brush. Be careful not to remove any metal. Do the same to the cylinder head. Rotate crankshaft and inspect valves for wear or damage
Compare new head gasket to old to confirm it is the right one. Install head gasket and cylinder head and start the holding bolts by hand.
Then while cross tightening (first one side, then the opposite side) to manufactures specified tightness, in increasing tensions. Do not tighten each bolt all at once as this can warp the head

Valve Clearance
If the clearance is too great, the engine will be noisy (loud tapping). This can cause wear to camshaft and valve lifters in the contact area. Push rods can become bent. Valve timing is changed, resulting in poor engine power.

Valve clearance clearances are set with a feeler gauge. Spec sheets provide the information for each particular engine. If the clearance is too little, valves will not seat properly and heat will not be transferred properly resulting in burnt valves, low compression and poor engine power.
Check manual for correct clearances. Typical clearances is .006 intake, .012 exhaust.

Adjusting Points
On most small engines the points are located behind the flywheel. If the points are located behind the flywheel, remove the flywheel and remove the spark plug; this will make it easier to turn over by hand. Rotate the crankshaft until the points are open their fullest. Using a feeler guage, adjust the point gap so the feeler guage just slips between the points with a little friction. If you are setting them to .020; then 022 would feel much to tight and 018 would just slip in way to easy. Locate the timing mark stamped on the engine. There should be two marks, one relating to top dead center and the other some degrees(11-20) before top dead center. If you are setting the timing to the BTD degrees mark, then the points should just open as the timing mark just passes the timing mark. If you want to get precise measurements, then place a ohmmeter across the points and watch for the deflection as you turn over the engine by hand. Follow the correct point setting and timing specs for each engine. Note, oil acts as an insulator to electrical current. If oil settles on the breaker points, its high resistance will prevent electrical current in the primary circuit. There is a seal on the point plunger to prevent oil from entering the breaker point area. A seal can be added if there is not one. The contact surfaces of the points must match exactly and squarely; adjust if necessary.

Testing Condensers
The condenser is constructed of a metal foil strip, which is wrapped in a circular fashion within a metal case, but insulated from each other. The tin foil accepts an electrical charge and holds it for a while. If there is a short between the metal foil and outer case, or the wire lead is broken, the condenser is bad. A quick test to determine if the condenser is good, is to use a multimeter and set it on the highest resistance range ( X3). Touch the meter probes onto the case and center lead of the condensor; you should get no short reading, any reading is bad. Now reverse the meter leads and touch the case and lead again. The voltage within the meter will have slightly charged the condensor, if it is good. The meter arrow should deflect momentary indicating the condenser did hold a charge. Each time you reverse the test leads of the meter to the condensor, a small bounce deflection of the needle of the test meter should take place. Blackened breaker points is an indicator that the condensor is bad.

Rusted Metal Gas Tanks
Gas tanks that are rusted will eventually plug-up the jets in the carburetor. To clean out the rust, sand blasting is the best option. I have at times just removed all the gasoline from the tanks and flushed it out with water, add about a cup full of clean water with a drop of liquid dish soap, then placed a handful of 3/4 inch or smaller, crushed rocks into the tank. Place the lid back on and shake it until your arm feels like it is going to drop off. The rocks bouncing around will knock off the rust. Dump out the rocks when you are finished, flush out with water and let dry before re-installing on the engine.

Changing Oil
At least once a year you should change the oil (lawnmowers) when used once a week over a period of four months and more often with heavier use. The oil reserve in a small engine is about a liter of oil, or less. There is no filter to help clean the oil, so it becomes saturated with carbon and burnt particles. The lubricating qualities are lost and this causes rapid engine wear. To drain the oil; locate the drain plug on the lower part of the engine and remove. Drain into a container, replace the plug and refill with clean oil. Check the dip stick several times when filling, so as not to overfill.
Motor oil becomes problematic at about 400 degree F; don't overlook the importance of keeping the engine cleaned to reduce the build-up of heat.

Choke Adjustment
The choke must be adjusted so that you can control the choke to fully open and fully close. To adjust; loosen the cable hold down bracket near the carbureter and slide the choke cable either up or down to get the full action of the choke. When starting an engine do not leave the choke on too long as raw fuel left in the cylinder will dilute the oil around the piston, which can cause piston scuffing because of insuffient lubricating.

Keyway
The crankshaft on most small engines are secured to the flywheel by a key within the keyway on the flywheel. If the key in the keyway is bent by some tramatic force, such as a lawnmower blade hitting a rock; the key may become bent or broken. Even a slight bending of the key can cause the timing of the spark to change, resulting in hard starting or not starting at all.
When checking the key and keyway, check for cracks on the crankshaft and check the condition of the key. Replace them if you find any major damage. The tapered sections of the crankshaft and flywheel, must be clean and smooth, with no play between the two. Any slight burrs can be removed with a file. Check for any play or wobbling when the flywheel is placed on the crankshaft, it should fit firmly. If you have doubts about the condition of your flywheel key, replace it. It's not very expensive.

The maximum speed of small engines is 3600 RPM.

Horsepower
One horsepower is the ability to lift 550 pounds 1 foot in 1 second or 33,000 pounds 1 foot in one minute.

Typical Point Setting
American small engine--- .020 of an inch
West Bend ------------- .015 of an inch
Foreign makes ---------- .012-.016 of an inch

Typical Flywheel To Armature Gap
Outboard Armature to flywheel clearance ---- .006 of an inch
Under flywheel Armature to flywheel clearance ---- .012 of an inch
To test clearance on a under flywheel, use a strap wrench to hold the flywheel when removing the retraining nut. Wrap the armature with two layers of black electrical tape without stretching too much. Place the flywheel in place and you should feel a little friction when you turn the flywheel. Remember to remove the tape when the testing is complete.

Heat
Large quantities of heat are produced in the combustion chamber, where temperatures can reach 2000 degrees F. A third of this heat is used for work, a third goes out the exhaust and the other third heats the engine.

Lean Running
- a slow falling and building of engine RPM
- Lack of power
- Carburetor spit-back on sudden acceleration
- Engine picks up speed with choke slightly on
- spark plug porcelain bright white

Rich Running
Black smoke in exhaust
Black soot on sparkplug tip
Lack of power

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A dozen pulls and it didn't start! It's time to do the three point check to find the trouble. Find the problem in three easy steps.