Starting a cold four stroke engine is sometimes easier than starting a two stroke engine. Although the heavy oil may make manual starting feel heavy and difficult. To pull the starter on a ten horsepower snow blower in freezing weather, for example, you must brace your feet firmly and exert considerable force. If you have heart problems or other physical limitations I suggest an electric start kit if one is available for your engine.

Begin with the choke closed. Some four stroke engines will pop and stutter like a two stroke, a sign that the choke should be opened part way to lean out the fuel mixture with more air. Others will start and run sluggishly, accompanied by black smoke-signifying that the mixture is still too rich with fuel. Open the choke gradually until the engine smoothes out and the black exhaust smoke clears. As with old cars, if the engine starts to die give it a bit more choke, and if it bumbles along ease off the choke.

Although some two stroke engines have primer's and so-called automatic choke's, it's still helps to know the typical sounds of over rich and over lean conditions. With most small two stroke engines such as chain saws, the conventional starting technique calls for closing the choke when the engine is cold. With the ignition on, two or three pulls should produce a muted pop or stutter which means fuel is reaching the combustion chamber.

Continuing to pull the starter with the choke closed will almost always result in flooding and no start. Listen for the first sounds of combustion and then open the choke. If a wide-open choke produces a brief run during which the engine seems to grow weaker and die, repeat the sequence but this time open the choke only about halfway. The engine should start and as it gradually warms up you can ease the choke open further until it runs smoothly with the choke fully open. On some engines, such as a snow thrower in cold weather, you may have to work with a partially closed choke for several minutes until warm.

As a matter of normal practice, try starting a hot engine with out the choke. If it doesn't start with one or two pulls, try partially closing the choke. Some engines, especially those with diaphragm carburetor's mounted on top of the tank, seemed to require full choke starts to establish fuel delivery even when warm or hot. In other cases shutting down a hot engine for a few minutes may cause the fuel in the line and carburetor to vaporize from engine heat. In effect, the fuel boils out of the carburetor or creates a vapor barrier in the line-a condition called vapor lock. Again, a choke usually helps.

Most small engines have rather individual starting characteristics. What works well for one may not be suited to another. The trick is to listen and learn to identify the various sounds and the feel of an engine during starting.

A badly flooded two stroke engine often sounds wet and what you're hearing is excess liquid fuel in the crank case and combustion chamber. The quickest cure is to remove the spark plug and pull the starter several times. Dry off the plug if it's wet. One sure sign of flooding is a bloop of blue flame when you pull the starter with the plug grounded next to the plug hole. That's excess fuel being expelled. If you replace the plug after the blue flames subside, you may be able to start the engine or you may have to wait until more fuel evaporates.

Hand starting a four stroke engine of five horsepower or more when the temperature is 15 below zero will usually be much harder than starting that same engine on a warm summer day. Even with an electric starter, your small engine may be more stubborn than the one in your car. Stale or summer grade gas, low cranking speed, or drag from something like a belt tightener clutch or hydrostatic drive transmission could be to blame. The main factor, however, is that you're only working with the power impulses from a single cylinder. If the first power stroke doesn't produce enough torque to rotate a 4 stroke engine through one and a half more revolutions against internal friction and drag loads the engine may pop but will not start. This is specially true for hydrostatic drive garden and lawn tractors if the drive cannot be disengaged. Even though the drive is in neutral, the engine will fire repeatedly but won't start.

Use thinner oil. Use SAE 30 above 32 degrees, below 32 degrees use 5w30, and below 0 degrees use ten weight diluted with ten percent kerosene. The heavy oil should be drained while hot, the thinner oil put in, and operated briefly before cold weather. Trying to drain cold SAE 30w oil at sub freezing temperatures is tedious and still leaves the thick oil on the piston and bearings.

Apply heat. Many engines have long dip stick tubes. If you can slide a dipstick heater down into the oil a few inches you should have no trouble starting. With a hydrostatic tractor drive, you'll find a dip stick heater does far more good if you put it in the transmission oil check hole rather than in the engine oil.

If you don't have a dip stick heater, simply place a heavy-duty soldering iron along the engine base so both the oil and the carburetor receive some heat.

Battery starting capacity drops sharply in the cold, so it's important that the terminal connections are bright and secure. It is also a good idea to keep a trickle charger on the battery for at least a few hours before starting. The electro-chemical action will warm the battery and greatly boost its cranking power.

Starting problems ignition, fuel system, and compression

The first questions to ask yourself are. Do I have ignition? Is fuel getting to the combustion chamber? Do I have compression?

Probably the first check you should make is the easiest-namely, removing the spark plug, re-connecting it to its lead wire, then placing it on top of the cylinder head and pulling the starter. This is also your first step. If you see a healthy, bright blue spark, you probably have ignition; if not you'll have to dig into that, but for now assume you have a good spark.

If you doubt that fuel is reaching the combustion chamber, try a brief shot of starting fluid into the carburetor throat with both choke and throttle open. Crank the engine immediately since the fluid evaporates fast. If you get a short, fast run on the fluid you know you are getting ignition and probably have adequate compression but are not getting fuel from the carburetor.

At this stage, a second trick may work if the carburetor jets are slightly plugged with gum or oil. Repeat the above start with the fluid but have the choke closed or snap it closed during the brief run. In many starting problems with engines out of storage, this was all that was needed to clean out the Jets for the rest of the season. Once the engine was running, the flow of fuel flushed the Jets clean. If you try starting fluid on a chainsaw, be sure you have the saw held down firmly. Sometimes the engine will kick and pull the rope hard enough to spin the saw toward you.

Assume for the moment that the starting fluid did not help. You observed a spark but providing fuel to it did not produce even a brief run. Begin your compression check by removing the spark plug wire and rotating the flywheel with your fingers or with the manual starter. You should be able to feel whether the piston is building up compression or not. If the flywheel spans easily through two revolutions with little resistance or bounce, you can suspect a blown head gasket, stuck piston rings, or a stuck or burnt valve.

Most small engines use magneto ignition whether the system is solid-state or traditional breaker point, this means that magnets are built into the flywheel rim and the engine generates its own electricity with out a battery or other external power source. A few engines, particularly Kohler, do use battery ignition, but these are mainly industrial applications.

This is exactly the opposite of battery-powered systems such as the one on your car. With battery power the switch must be closed to feed battery power to the circuit.

Many small engine starting problems relate to the spark plug. The plug may be fouled, internally conductive, or the wrong heat range. The spark plug is always the first thing to check when starting problems arise. Check for fouling. Dampness from outside storage, as well as dirt and grease from fingerprints, may cause a plug to miss fire. Also, condensation inside the cylinder or intake valve port in a four stroke engine can cause a drop of water to be splashed on to the plug electrodes and short out the plug. A spatter of oil or minute fragment of carbon or other combustion debris can do the same thing, particularly in two strokes.

If the plug looks oily and the engine is a four stroke, it suggests that the piston rings and or the valve guides are worn.

On a two stroke engine a little oil is not unusual as long as is just a little. Most four stroke engines will show light gray or reddish tan deposits on the spark plug core nose. If these are heavily deposited into space between the core nose and the outer shell, it's not really worthwhile to try to pick them out. In fact, cleaning spark plugs is generally a waste of time, and sand blasting is definitely bad practice. There's just too much chance of sand wedging up in the plug and then dropping out and damaging the cylinder and piston.-if you've logged over 50 hours on a four stroke spark plug or over 20 on a two stroke-replace the plug. Many deposits around the core nose are conductive and can provide a path to ground for the high voltage energy, again, shorting out the spark gap.

Spark plug reach. The length of the threaded portion of the plug is called its reach. Some chainsaw engines and the like may require plugs with only a 1/4 inch reach. Others may require as long as 5/8 inch, and there are several lengths in between. If you install a plug that is too long, the piston may strike it and cause severe damage. A more likely condition is a plug that projects only a thread or two past the inner face of the cylinder head. Under the heat of combustion, such projecting plug threads or deposits on them can glow, and ignite the fuel prematurely-a condition called pre-ignition. Besides reducing power pre-ignition often leads to detonation, or the uncontrolled burning of fuel commonly called pinging or knocking. The possibly consequence, in small engines with light aluminum Pistons, is often a hole in the piston Crown or a burned off piston edge. The same damage can occur if the plug reach is to short. Now the uncovered threads in the cylinder head become hot and glowing, again causing pre-ignition and detonation.

Both situations also cause trouble when removing or installing a new plug. Deposits or corrosion on an extra long plug will prevent free turning in the threads, making it extremely hard to remove. Such deposits can literally tear out the threads of an aluminum head if you force the plug. Instead, try to get some penetrating oil down into the threads and gently work the plug back and forth with the socket wrench.

If the old plug was to short, the deposits in the last few threads will prevent the new plug from seating against the gasket properly. Run a tap or cleanup tool all the way through until the threads are formed cleanly.

Spark plug heat range. You'll hear plugs referred to as hot or cold, and sometimes medium plugs. That has nothing to do with the intensity of the spark delivered, which remains the same. It does relate to the temperature at which the plug core nose operates. If the plug core and electrodes run too hot they will erode or burn away quickly and may cause detonation. If these parts run too cold they will collect deposits and foul. A plug of the proper heat range will more or less self clean without rapid erosion.

Sometimes an engine manufacturer may have anticipated a heavier load on the engine than the job you're doing and specified a cool plug. If your plug rapidly builds up deposits and causes starting problems, try the next hotter plug. Conversely, if your plug shows white blistering and rapid erosion of the electrodes, try a slightly cooler plug.

Anti-RFI plugs. In many areas, particularly in Canada, stringent laws prohibit equipment that produce high radio frequency interference. In most small engines RFI is suppressed by resistor type spark plugs. If the designation code on your original plug includes the letter R, be sure the one on your replacement plug does too.

Removing stubborn spark plugs. Even plugs of the proper heat range and reach can sometimes be unusually difficult to remove. If the plug and gasket are gas tight, it's unlikely that penetrating oil will get down into the threads. The only real choice is to use a good socket that fits the plug, a sturdy flex handle and a strong pull. A 1/2 inch drive wrench may be necessary. Just barely break the plug loose. Then, if it doesn't come freely, the penetrating oil may help as it can now get past the gasket and down through the threads.

Baked and hardened fuel gum in the threads can also make them stick. If the plug wasn't quite tight combustion gases may have worked up along the threads and literally glued the plug in place. For that reason, it doesn't hurt to add a little carburetor cleaner to the penetrating oil while its soaking. Even kerosene will help if you gently work the plug back and forth.

Gapping the spark plug. The gap between the spark plug electrodes should be checked both before installing a new plug and when you've removed a used plug that appears to be good. Consult your manual for the correct gap, and adjust if needed with a wire type feeler gauge/bending tool. Do not force the gauge through it; it should only have a barely perceptible drag.

With a used plug, the gap has usually opened somewhat and the electrodes may have lost their sharp corners and edges. Unless the outer electrode is so worn as to show a notch, use the bending tool on the feeder gauge to carefully move it away enough to introduce a thin, flat ignition file. You can also been the outer electrode with the tip of a small screwdriver levered against the metal outer shell. Never try to move or bend the center electrode. Instead, file its tip so that it is flat and the edges are sharp. Also file the tip of the outer electrodes to produce a sharp, square edge. It takes less ignition energy for the spark to jump between two sharp edges than between two worn, blunt surfaces.

You should be able to run the plug in with your fingers or very light wrench action until it seats on the gasket. On new plugs, standard recommendation for final tightening is to pull the wrench handle 1/4 turn after the plug seats firmly on the gasket. On used plugs where the gasket has already been in contact, pull just hard enough to feel the plug turn firmly against the gasket. In rare applications with no gasket and a tapered seat in the head, 1/6 turn is recommended.

Non-plug ignition troubles

once you know you have a good spark plug, yet still don't have a spark or one hot enough to start your engine, check the high tension lead wire to the plug at the point were it emerges through or from under the blower housing. Gently tug the wire out

about 3/4 of an inch and examine it all around. Look for chafing, cracking, or abrasion, which may be letting ignition energy leak away. In such cases, testing the plug for spark outside the engine may indicate no problem, but inside, the greater resistance across the gap caused by the compressed fuel charge may be making the plug misfire. If you get a spark with the plug out, re-install it and, with the wire still pulled clear, try starting the engine. You may be surprised to see it fire because the energy leaking out of the lead wire has found its way to the plug.

Nearly all high voltage leads are now molded or sealed into the coil, and you might need a new coil and wire assembly. But first, try coating the chafed spot with silicone sealer. Don't use the metallic variety. Let it cure overnight and it will probably last as long as the engine.

PRIMARY WIRE PROBLEMS

 On many mower and tiller engines the remote throttle control is marked start, run, slow, and stop. Move the control to stop and the throttle linkage slides a little switch closed and shorts out the ignition system. Such a switch will probably be on or near the carburetor and will have a light gauge wire running to it. This wire is usually just clipped to the switch and is easily pull or broken off accidentally. This seemingly innocent wire is the magneto primary ground wire and if it's touching bare metal your engine will not start. Sometimes just mowing or working under low shrubs will snag it.

If your engine won't start with the wire in place, try slipping it free of the clip on the switch. Wrap a fold of tape over the bare end and see if the engines starts. If it does, the switch is defective or foul. Clean it with a small brush and solvent and examine it carefully. You may find that the sliding member is then, damaged, or corroded. Plan to get a replacement. Meanwhile, you can start and operate with the ground wire taped. Stop the engine with the choke or by shorting the plug with a screwdriver if it has an open terminal.

Chainsaw switches. On other types of equipment such as chainsaw's, a small manual switch stops the engine. Sometimes you can get at the terminals of the switches easily, and other times you have to disassemble half the machine to open up the handle. Unless you're prepared to open up a tight package of controls with many small parts, take the saw to a dealer.

Remote switches and interlocks. On some equipment it's easy to spot a low tension wire running out to a mower or tiller handle or under the seat of a rider mower or tractor. These are also magneto ground switches. If the switch its self is buried, it may be easy to snip the wire at a handy point and see if you get a spark. Later, with a new switch or other trouble source revealed, you can solder and tape the wire back together. In addition to the main switch and the under seat safety switch on many machines, there may be several other interlocks connected to the ignition ground and possibly the starter circuit. These may be somewhere in the implement drive clutch to prevent starting with the cutter engaged, and/or near the shift or brake pedal/clutch to prevent starting except in neutral with the foot brake depressed. Usually, these switches are connected with slip on terminals. Simply disconnecting these to be sure they aren't touching metal will enable you to check for ignition ground.

Don't overlook the point that although the switch may be in perfectly good shape, the wire leading to it may have been chafed or pinched in the machine chassis and be grounding out there. While you're checking switches and wires, also take note of other small wires and connections and try them for tightness.

INSIDE THE IGNITION SYSTEM

 When you've done all you can with external parts of the ignition system, the trouble is probably somewhere in the magneto itself. It could be a corroded or worn set of breaker points if your engine has them. It could also be a bad condenser or coil, or a bad electronic ignition module. By now, unless your ignition system is really out of order, you should be able to start-in three pulls or less.

TROUBLE SHOOTING THE FUEL SYSTEM

begin by taking a quick look at the carburetor with the air cleaner off, and be certain that the governor action and throttle controls have really opened the throttle wide after you opened the control lever. If there's a choke plate or other choke device be sure or is closing properly. And try shaking the carburetor to be sure the mounting nuts or screws are secure. Many hours have been wasted trying to start or adjust a carburetor when all that's wrong is that it is loose and leaking air at the mounting flange. Also try closing the choke when turning the engine. You should be able to see you raw fuel in the carburetor throat. If there is fuel, although the carburetor may be misadjusted or have some other trouble, the engine should at least pop or backfire.

Check tank to carburetor connections. If you get only short runs of a few seconds after using starting fluid, you can be almost certain of one of two conditions, and maybe both. First, the fuel may not be getting from the fuel tank to the carburetor. If a rubber or metal line runs from the tank to the carburetor, as it does on a typical gravity feed system, loosen the line connection at the carburetor and see if fuel flows. If not, the line could be plug, but more likely a small screen or strainer in the tank is blocked with fuel gum. Drain the tank out in the open away from the house, providing a receptacle for the gas. Then remove the strainer-usually together with a shut off valve from the bottom of the tank. Usually all that's needed is a good washing and brushing with lacquer thinner or carburetor cleaner. Clean until you can see through the screen and blow air through it and the valve freely. If the areas and in-line filter, either replace it or temporarily splice the line with a piece of metal tubing and clamps.

Check the fuel pump. If your engine has a fuel pump, the fuel may be blocked there. With the line to the carburetor disconnected, spin the engine with the starter and watch for fuel delivery. If no fuel appears at the pump outlet, a strainer or screen may be plugged at the pump. The pump diaphragm or valves may also be defective or stuck with gum. Only careful disassembly and inspection will reveal this. Always watch for the small washer and seal ring that are under the anti-vibration spring on most carburetor needle valves. Often they're down in a pocket and stay in place when the valve is removed.

Tank top carburetor's

This common type of fuel system is easy to spot because the carburetor's body mounts on top of the tank. Such carburetor's have extension tubes that go down near the bottom of the tank and pickup fuel through a screened pickup. Some of these suction less carburetor's have a rubber/cloth diaphragm to aid in the pumping action. These starting problem could be caused by the diaphragm and associated parts, and these are easily replaced. First, try removing the carburetor from the top of the tank and cleaning the screen and check valve, if they're gummed up. You will need a new mounting gasket you may have to take off the tank and carburetor as a unit and then separate the carburetor from the tank. This is not difficult and provides a chance to check the connection between the carburetor and the engine intake port. Not all carburetor's have flanges secured by nuts or screws. Some tank top carburetor's simply slide off a tube like connection at the intake. This joint is sealed by a synthetic 0-ring if the ring has deteriorated, cracked, or been damaged you've probably found your trouble. The only cure is a new o-ring.

CARBURETOR CLEANUP

let's assume that when you loosen the fuel line to the carburetor it was apparent that fuel was getting that far. The remaining trouble spots are commonly the main and idle jets. Some carburetor's have no adjustment screws and cannot be cleaned without disassembly, but many have two knurled and slotted screws for the idle and main Jets. These screws terminate in needle like tips and extend into the Jets. Screwing them in or out varies the amount of fuel that can pass the Jets.

Removing the idle and main Jets screws

adjusting such screws is a fairly critical process, and since your engine had been running previously the adjustment positions are probably about right. So before removing the Jets screws, first turn them in very carefully and count the turns, half turns, and quarter turns it takes to bottom them. Never force these screws and be alert for the feeling of bottoming. Make a note of the turns you needed and then back the screws all the way out.

Many such screws are sealed with small O-rings too or rubber and brass washers where they enter the carburetor body. Watch carefully for these small parts since their easy to lose. Also note the anti-vibration springs. They may not be interchangeable between the screws. In fact, on some carburetors is it is possible to accidentally switch the main jet and idle Jets screws. Keep track of then by pushing them through a piece of paper and labeling it.

Cleaning the Jets. After removing the screws, examine them carefully for signs of stickiness or gum and discoloration at the tips. If you find it, you've probably located your trouble. Use carburetor cleaner or lacquer thinner and gently wipe the needle tips clean. This action may get you going, and once running the fuel may even clean out the Jets down inside the carburetor. But if the Jets are firmly clogged with gum, you will still have trouble.

One possible solution is to squirt a drop of carburetor cleaner into the Jets with the needles out. Try using something such as a plastic cocktail tooth pick to go down into the jet and carefully stir the cleaner around. Do not use wire or a drill. Now, replace the screws, adjust them to their original settings, and try to start the engine. There is an excellent chance it will run, though you may have to readjust the screws settings because the Jets are not perfectly clean.

The main hazard with that procedure is that you are introducing a very strong solvent into the carburetor. If the engine starts and runs there's no problem because the fuel should wear away the solvent residue. If the engine does not start, the solvent may find its way through the carburetor and seriously damage plastic or synthetic rubber over a few days time. The larger, float bowl types are not likely to suffer greatly from solvent since their parts are usually metal, but the small diaphragm carburetors on chain saws, trimmers, and the light may be vulnerable.

If you cannot get your engine to start and run after cleaning the jets from the outside, there is little choice but to disassemble the carburetor and find the source of the trouble. Here, careful work and cleanliness will probably get you by with flying colors; but unless you feel fairly confident you may be better off removing the carburetor and taking it to a repair shop.

TROUBLESHOOTING COMPRESSION PROBLEMS

with the spark plug wire disconnected, turned the crank shaft and listen carefully for hissing sounds at the carburetor inlet and exhaust outlet. Leaking valves are often signaled by hissing or blowing noises. If you hear no such noises but compression still seems low, try squirting a little engine oil into the spark plug hole, replace the plug, then carefully turn the engine. If you feel the compression improve markedly, you've probably got a piston ring or cylinder problem. If the engine was running reasonably well last week it's unlikely that its suddenly got sick sitting idle for a few days. But if you haven't run it for months, the rings might be stuck.

Before becoming too alarmed, try removing the blower housing than check the head gasket. More fruitless hours are spent trying to start engines with blown head gasket than might be imagined. That's because the owner very often does get the engine started, finally, and it seems to run fairly well. The reason is that during starting the engine is turning slowly and there's time for the compression to leak away. Once running the action is so fast that there's little time for leakage.

CHECKING THE HEAD GASKET

 One way to check a head gasket is to squirt or brush a little oil around the joint between the top of the cylinder block and head. The reason for removing the blower housing was to gain access to the area around the exhaust valve, the most likely point for the gasket to burn out the exhaust valve will be located very near the exhaust pipe connection. Crank the engine over vigorously and watch for bubbles in the oil any at all are a sure sign of gasket leakage. Another quick check is to fit a properly sized box end or socket wrench on each head bolt in turn. Pull firmly, but not so hard that you actually turn these bolts farthest from the exhaust valve-a less likely trouble area. If you test each bolt this way and come onto one or two that seem to yield slightly compared to the tightness of the others, you've probably found a bad head gasket. Although you may get the engine going just by snugging down the loose bolts, this is bad practice and can distort the cylinder wall and head and cause much more serious problems. The head gasket must be replaced.

LEAKING VALVES