Two stroke engine repair and maintenance pdf download

I down loaded your mariner service manual but I didn't get the part hp 4 cylinder engines powerhead part 4 b for hp motor. Tramper Friday, 08 January Update to first message.. Not sure about last didget Explorerone outlook. Tramper Thursday, 07 January J Strickland Thursday, 10 December I need a printed original Mariner Magnum service manual.

I need a Mariner Service manual for a 50hp, 2 cycle, 3 cylinder. Peter Thursday, 08 October Cheers Pete. If you have any questions, please contact us. E-mail: downloadboatmanuals gmail. Motors Boats. Mariner outboard engines: service and owner's manuals PDF. This company manufactures its products in the United States of America: Outboard motor Mariner is represented mainly in such categories as sports engines, water-jet engines, as well as standard boat engines Mariner and Verado; all these outboard engines managed to prove themselves very well.

They are ordered by boaters from different countries. Moreover, some models can be purchased for quite reasonable money;. The mariner outboard motor is available in approximately countries around the world. Read also. Total Comments: 0. Sign in:. Rate my site. Ever-tightening regulatory constraints leave manufacturers with two options: switch to four-cycle engines or else figure out ways to clean up the traditional product Table The company subsequently collaborated with RedMax-Komatsu Zenoah to produce a heavy-duty version of the engine.

Honda, recognizing the opportunity, entered the market with its overhead cam GX22 and GX Thanks to mist-type oiling systems and diaphragm carburetors, these little four-bangers operate at any angle.

But four-cycle micro engines have their detractors. According to a spokesman for Robin America, a four-stroke cc engine is, on average, 1. In contrast, a Husqvarna two-stroke trimmer of the same displacement weights The valve gear required by four-stroke engines consists of 25 or 30 parts, most of which require precision machining and heat treating.

But four-cycle engines need frequent oil changes and level checks, chores that contractors cannot depend upon their field personnel to perform. In addition, there are reports of problems with these new engines when operated off the horizontal.

But the advent of hybrids, which combine some of the best features of two-strokes with superior fuel economy and less pollution, shifts the balance.

The dry crankcase permits the engine to run at any angle and eliminates worries about oil levels and change intervals. And the four-stroke cycle, which allocates a full piston stroke to scavenging, significantly reduces HC emissions without the need for a catalytic converter.

Figure shows the general layout. The upper crankcase, cylinder barrel, and head are integrated into a single aluminum casting. Overhead valves operate from a single cam lobe, a feature that reduces engine size and weight Fig. The cam also incorporates an automatic compression release. Oiling is accomplished by patented, two-stage process.

As the piston rises toward TDC, it creates a partial vacuum in the crankcase Fig. The fresh charge, consisting of a mix of fuel and lube oil, enters through the inlet pipe 1 and bypass port 2 and passes over the cylinder head on its way to the crankcase.

En route, the fuel charge wets all moving parts, including the critical camshaft lever. Cleaner two-cycle exhaust Survival of the two-stroke engine depends upon finding ways to limit HC and CO exhaust emissions. Currently two approaches are used: stratified charging and exhaust after treatment. The horizontally split crankcase is a welcome feature that provides easy access to rotating components.

A single cam lobe 4 , driven at half speed through the crankshaft gear 3 and through a pivoted lever 5 , pushrods 6 , and rocker arms 7 actuates the exhaust 1 and inlet valves 2.

Generously sized drive gears, coupled with antifriction bearings, are designed for durability. Stratified scavenging One way to sanitize two-strokes is to purge the cylinder with air before introducing fuel. The RedMax Stage 1 incorporates two transfer ports, each of which is fitted with a reed valve that opens to the air-only carburetor bore. An additional reed valve connects the second, or fueling, carburetor bore with the crankcase.

As the piston uncovers the exhaust port, residual gases blow down and leave a vacuum behind in the cylinder. Transfer-port reed valves open to admit purge air from the carburetor. Meanwhile the falling piston builds pressure in the crankcase and in the transfer ports.

The downward movement of the piston pressurizes the crankcase. Oilimpregnated fuel then leaves the crankcase, lubricating the critical valve-gear parts for a second time Fig. Air no longer enters the cylinder, which then fills with the fresh mixture from the crankcase. On the other hand, cylinder filling suffers because some scavenge air remains in the cylinder after the exhaust port closes.

The prototype version developed slightly less power than a reference engine with conventional porting. NOx emissions, fueled by the additional oxygen, showed a small increase. Unlike the EPA, California regulators take an active part in the development of technology. Surprisingly enough, the Strato-Charged RedMax encountered buyer resistance.

Potential buyers interpreted the unobtrusive exhaust note as evidence of lack of power. As the piston falls, the pressurized fuel mixture flows out of the crankcase and back to the intake pipe for induction into the cylinder. In the process, moving parts are again wetted. The Walbro WYA carburetor features a mm bore, an adjustable idle jet, and can be fitted with an accelerator pump.

While designed for stratifiedcharge two-stroke engines, this carburetor can also be adapted to four-strokes. Cleaner two-cycle exhaust 27 made converts. The engine has a mm bore and a short mm stroke for a displacement of 24 cc. With a dry weight of only At first glance, the PureFire could pass for any other piston-ported engine. Air and fuel are drawn into the crankcase during the upstroke and forced out through transfer ports on the downstroke.

Fuel and air move out of the crankcase and into a channel that leads to the transfer ports. A smalldiameter orifice connects the crankcase cavity with the transfer-port feed.

This orifice gives velocity to the charge, which absorbs heat in its journey to the transfer ports. Velocity and heat assist in fuel atomization, a precondition for efficient combustion. The photo on the cover of this book illustrates Purefire gas flow. HC and CO emissions that survive are oxidized in the catalytic muffler. The catalyst consists of a thin veneer of platinum, palladium, or rhodium applied over a ceramic or metal matrix. A two-way converter, that is.

NOx emissions do not present much of a problem for carbureted two-strokes. In the presence of heat, the converter oxidizes hydrocarbons into carbon dioxide and water. Other reactions involving CO release water and hydrogen.

Consequently, the converter runs cooler and should last longer. A catalytic converter intensifies maintenance requirements. Rich mixtures resulting from improper carburetor adjustments or dirty air filters must be avoided.

Excessive oil or the wrong type of oil fouls the catalyst. And finally, silicone adhesives or carburetor cleaners containing lead, phosphorous, or silicone must not be used.

But, even with these precautions, converters are sacrificial items that need periodic replacement. Marks of quality Designers of small motorcycle engines are a conservative bunch and rarely deviate from a pattern that was established during the s.

Almost without exception, these engines have vertically split crankcases, ball main bearings, one-piece connecting rods, and loop-scavenged cylinders.

Since design is frozen, variations in quality come down to the choice of materials and the precision of manufacture. Japanese and European makes are the obvious leaders, with Chinese and East Indian bikes trailing far behind. While many readers might protest, the EPA calculates the useful life of small motorcycles those displacing between and cc at 12, km mi. Designers of handheld equipment are much more flexible, in part, because the machines are tailored to very different markets. But the money saved will soon be spent on repairs.

Find out what local landscape contractors use, since quality involves more than the brand name. You want a machine from a nearby dealer, who has a good parts inventory and who honors warranty claims. What is the useful life of handheld equipment? Manufacturers are coy about this question, but we do know that the design life—the life engineers try for—is hours for professional quality tools.

Echo insists that their engines, which are not dramatically different than other upper-echelon products, have a design life of to hours or more. The factory warranty period reflects how well the design life goals are achieved. Good-quality garden and construction tools carry a warranty of 2 years in private use, 1 year commercial, and 90 days rental. Some offer longer periods and certain components such as ignition modules and driveline parts may be covered for the life of the equipment.

Chainsaw warranties typically extend for a year of private use. Another indication of the way manufacturers judge the longevity of their products has come about because the EPA insists that exhaust emissions be tested twice, once when the engine is new and a second time at the end of its useful life.

According to the rule, published in 40 CFR, Chapter 1, The choice is between , , and operating hours. Useful life is calculated on the basis of engineering evaluations of wear, surveys of engines in the field, customer complaints and other hard data. No manufacturer has opted for the hour test. Cheaper and almost certainly less durable engines use crankshafts cantilevered off of a single bearing Fig. Some manufacturers merely chrome the piston. Tanaka and a few other manufacturers allow cylinders to age before final machining.

Two holddown bolts are a proscription for air leaks, although it must be said that the RedMax two-bolt arrangement with locking tabs gives no trouble. Low-end products get by with one.

Hanging the crankshaft off a single main bearing dramatically reduces costs. The vestigial crankshaft requires little machining and the crankcase cover can be made of plastic.

Tanaka PF is an example of design quality. Few, if any, low-priced engines incorporate thrust washers. One manufacturer goes so far as to eliminate the circlips that prevent the wrist pin from walking into the cylinder bore.

The easy way is to make the transition is mount the cutter head on a curved shaft. A flexible cable, a kind of jumbo speedometer cable, transmits power. The cable whips and quickly destroys its bushings. Quality machines employ a solid steel drive shaft, about 7 mm in diameter, and bevel gears at the cutter head. The ends of the shaft should have proper splines D-shaped or squared ends need not apply and ride on ball bearings.

Oil-lite bushings are a distant second choice and nylon bushings are hardly worth mentioning. But be aware: Some midmarket trimmers have the prerequisite gear box, but drive through a flexible cable. The learning curve Things learned from working on automobiles and four-stroke lawnmowers do not always apply to two-strokes. This is why small-engine shops usually have a resident two-stroke guru, who can be called on when simple fixes fail. The basic problem is getting rid of the heat generated by engines that fire every revolution.

Catalytic converters add to the heat load as does the scale effect. Because of reduced surface area, the smaller the engine, the more heat retained. Combine heat with the high oil consumption of two-cycle engines and we have a recipe for carbon production. After long use, carbon deposits in the exhaust port and muffler throttle the engine.

Carbon also collects in the ring grooves, where it robs the rings of their elasticity. If rings cannot flex, they cannot seal. Large fragments of carbon, embryonic diamonds, can break off and score the bore and piston. Most scoring occurs in areas adjacent to the exhaust port, which runs hot and sees little by way of lubrication. As a point of interest, the bridge—the knife-like rib running vertically between the exhaust ports—is the hottest part of the engine.

But without a bridge, the rings would expand to fill the port and snag. Heat also distorts plastic shrouding, causing air leaks and converting fuel lines into something resembling uncooked spaghetti. Compromised fuel lines can leak fuel or air. Wear and scuffing that go unnoticed on larger engines take on major importance when cylinder diameters are reduced to 30 or 35 mm. The ring seal also pressurizes the crankcase, a function that becomes critical during starting, when rpm is low.

Consequently a small two-stroke needs a minimum of 90 psi cranking compression. A four-stroke can be persuaded to run with 60 psi. Crankcase compression also depends upon the integrity of the crankshaft seals and, when fitted, the reed valve. And finally, there is the matter of carburetors. In order to operate at large angles off the horizontal, two-stroke engines have diaphragm carburetors with integral fuel pumps.

These carburetors are a world apart from the floattype units found on most four-cycle engines. To summarize, the differences between two-stroke gurus and ordinary mechanics are that gurus appreciate the importance of cylinder and crankcase sealing, check that rings are free to flex, look on fuel lines with suspicion, and have experience with diaphragm carburetors. Long-term storage At least half of the problems associated with two-cycle engines come about because of improper storage.

Do not open the throttle, since running dry of fuel also robs the engine of lubrication. Slowly turn the engine over several revolutions to distribute the oil. Replace the spark plug and reconnect the ignition lead. Inspect the fuel container for rust or varnish build up. Safety By their nature, gasoline engines pose risks. The fuel is highly volatile, mufflers and catalytic converters run hot, exposed parts revolve at high speeds, and, when confined in a closed space, the exhaust can be lethal.

Safety 33 Gasoline A U. Should it find an ignition source, the vapor trail acts as a fuse to convey the flame back to the container. Store fuel in an approved safety container—not a plastic jug.

Gasoline and other flammables should be stored in a locker, remote from the shop and house. Allow at least 5 minutes for the engine to cool before refueling or opening a fuel line. If working outdoors is impractical, make certain the shop is well ventilated and that no ignition sources are present.

Obviously one would not weld, grind, or smoke in the presence of fuel vapor, but one should also be aware that any spark, as from switching on a light, can become an ignition source. Before starting an engine after adding fuel, wipe up any spills, allow ample time for evaporation, and position the fuel container at least 10 ft 3 m from the machine. Although many mechanics prime engines by injecting gasoline into the carburetor or cylinder, many of the same mechanics are admitted to hospital emergency rooms for burn treatments.

When an engine must be primed to verify fuel delivery, use aerosol carburetor cleaner, never gasoline. Work outside, spray a tiny amount of cleaner into the air intake, and replace the air filter element before starting. The air filter acts as a spark arrestor. Do not use gasoline as a cleaning fluid. Gunk, available in aerosol cans from auto parts houses, does an excellent job of removing grease. But no solvent is entirely free of hazard; California health authorities classify Gunk as a carcinogen.

And finally, equip the shop with at least one Class B fire extinguisher. Water merely spreads gasoline and oil fires. Carbon monoxide Never operate an engine in an enclosed space.

When inhaled, carbon monoxide CO displaces oxygen in the bloodstream. Low levels of exposure result in nausea and headaches; higher levels are lethal. Rotating parts The business end of cutting and drilling tools present obvious hazards, and string trimmers, some of which turn 11, rpm, are by no means innocuous.

An engine secured in a vise by its crankshaft can, and sometimes does, start when rotated. If the shrouding is in place, the spark plug will not be accessible to a hammer; about all one can do is to clear the area and wait for the tank to run dry.

Open sparks While we routinely test for ignition voltage by arcing the high-tension lead to ground, this procedure entails risk. These testers confine the spark behind a transparent window. Recalls The U. Consumer Products Safety Commission website at www. Chainsaws have been recalled because of fuel leaks and flywheel disintegration. The muffler support strap on RedMax EB , EB , and EB backpack blowers has, on several occasions, torn away from the muffler, leaving a hole that diverts hot exhaust gases toward the plastic fuel tank.

The next chapter deals with troubleshooting, the critical skill that separates real mechanics from part changers. One continues to crank, hoping that somehow things will fix themselves.

We all do this, even those of us who should know better. At a naval research facility in Maryland the animals were routinely given slight electrical shocks, which they found pleasurable. One day the generator failed and the porpoises gathered round, whistling. How to relate malfunctions to engine systems is the subject of this chapter. Once categorized, repairs are simple. But understand that engines, even little two-strokes, are complicated enough to elude formula. We cannot see air leaking past a gasket or the failure of the spark plug to fire when screwed into the cylinder.

But we can assume that a torn gasket leaks and that a dirty spark plug misfires under compression. Odds improve with close observation, conditioned by an understanding of the importance of spark, fuel delivery, and compression. We can determine the presence of spark with an ignition tester but, short of laboratory instruments, we cannot measure spark voltage or energy. Too much fuel is as bad as too little.

The condition of the spark-plug tip is our gauge of fuel delivery. Small two-stroke engines need a minimum of 90 psi to start. Carbon accumulations in the exhaust ports and muffler rarely prevent an engine from starting, but drastically reduce power outputs. Tools and supplies Two-strokes are held together with metric fasteners, star-pattern Torx screws, and an occasional Phillips or Allen screw. Quarter-inch drive sockets are adequate for everything except the flywheel nut.

You will also need a spark-plug socket wrench, an ignition tester, and a compression gauge. Because they are torque-limiting, that is, designed to slip, Phillips screws present a problem. Striking the screwdriver with a hammer sometimes helps, but the ultimate persuader is a hammer-impact wrench.

Once you get the screws out, replace them with Allen or Torx fasteners. Supplies include fresh fuel, mixed with the correct amount of two-stroke oil, solvent, aerosol carburetor cleaner, and lint-free rags. Automotive brake cleaner is a potent, but toxic, degreaser that attacks paint and some plastics. And a word of caution: no amount of care can eliminate gasoline spills associated with draining fuel tanks and disconnecting fuel lines.

Ideally, the work should be done outside. If that is impractical, the work area should be well-ventilated and remote from pilot lights and other ignition sources. Wipe up spills promptly and allow plenty of time for traces of gasoline to evaporate before cranking the engine.

Keep a fire extinguisher handy. Preliminaries 37 Another tool, often overlooked, is a notebook small enough to carry in a top pocket. Preliminaries When an engine breaks down in the field, we try to zero in on the problem, fix it, and go on about our business.

In a repair shop, the urgency is usually less, and we can take the time to round up the usual aspects by replacing parts most likely to have failed. These include fuel leaks, weak compression, loose carburetor, crankshaft binds, and oil stains adjacent to gasket surfaces.

Such abortive attempts at repair complicate matters since you must now identify the original problem and whatever the hapless mechanic might have done wrong.

Gap to specification, which for most handheld engines is 0. A cam-type gauge gives less ambiguous readings than a conventional, flat-blade feeler gauge Fig. An acrid smell, a brownish taint, or globules of water in bottom of the container mean that the fuel system has been contaminated.

Flush the tank with hot water and detergent, replace the fuel filter, and overhaul the carburetor with new diaphragms, inlet needle, and gaskets as described in Chap. Use a hooked wire to retrieve in-tank filters of the kind found on handheld equipment Fig. The foam filter may be backed up with a pleated paper filter, which is a sacrificial element requiring routine replacement. You may also encounter a third filter downstream of the paper element.

This filter is a backstop to prevent dust entry when servicing primary filters. Narrow spark-plug gaps are the norm for small engines. In the case of this Wacker Neuson chainsaw, the 0.

OPEN E. To reduce the clearance, tap the side electrode against a hard surface B. Bosch 38 B FIG. Robert Shelby 39 40 Troubleshooting Tests Diagnosis begins with a series of tests and observations. These tools eliminate any fire hazard by confining the spark behind a transparent window. People with pacemakers or other medical problems should not expose themselves to electroshock. Solid-state ignition systems produce something on the order of 30 kV, open-circuit. That said, the traditional method of verifying spark delivery is to hold the spark plug against engine metal and crank Fig.

So long as the plug makes firm contact, voltage goes to ground through the engine and not the mechanic. A variation on this technique is illustrated in Fig. The spark should occur once during every revolution, as regular as a heart beat. No spark means a FIG. This method of checking spark leaves much to be desired. Plastic engine covers must be removed to access ground and unshielded spark presents a fire hazard.

With a spark-plug wrench inserted into the spark port, ground the spark plug against the wrench. Note that the wrench handle must not extend into the combustion chamber, if engine damage is to be avoided.

The mechanic has also taken the precaution of using insulated pliers. Test the integrity of this circuit by cranking with the kill-switch wiring disconnected from the ignition module Fig. Do the same for lights and other electrical components that may be present. Nor are electrical parts returnable after purchase. If you suspect that the module had failed, the only option is to test by substitution of a new, or known-good, unit.

In the wake of a whisker-induced ultra-light aircraft accident in England, Rotax replaced the engine, which used a single spark plug per cylinder, the dual-plug An ignition tester is also useful when diagnosing engines that run for a few minutes and then shut themselves off. Connect the tester to the high-tension 42 Troubleshooting FIG. The screwdriver points to connection on the ignition coil for the kill switch.

Robert Shelby lead, in series with the spark plug. Start the engine and watch the spark as the engine dies and coasts to a stop. Ignition should continue until the flywheel almost stops revolving.

If ignition ceases before shutdown, the ignition module has failed, probably because of heat. If ignition remains constant, then the source of the problem lies elsewhere, probably in the fuel system. Fuel system Fuel systems go wrong by delivering too little or too much fuel.

No fuel Crank a cold engine five or six times and remove the spark plug. If fuel is entering the cylinder, the tip of the spark plug will be wetted and smell of gasoline.

If the plug is dry, momentarily disconnect the fuel line to the carburetor. Unless there is an obstruction upstream—tank filter, screen, or clogged line—fuel should dribble out of the open line. Repair as necessary. When fuel is present at the carburetor inlet, the logical response is to bypass the carburetor. Remove the spark plug and spray a small amount of carburetor cleaner into the cylinder. Reinstall the spark plug and crank. If the engine does not start, the problem is almost certainly the spark plug or ignition module.

If it starts and runs a few seconds, we can assume that fuel starvation is the problem. Some malfunction prevents fuel from passing through the carburetor and into the combustion chamber. To further isolate the problem, remove the air-filter element and spray carburetor cleaner into the air horn. Replace the filter. Warning: Do not run an engine without the air-filter in place. Tests 43 If the engine runs until the aerosol is consumed, we can be confident that things downstream of the carburetor are normal.

That is, the reed valve functions and the piston seals well enough to draw fuel into the crankcase. If the crankcase seals leak, the leak does not inhibit starting. Since we have already verified that fuel is available to the carburetor, the problem must be in the carburetor itself.

Chapter 4 describes how to make the necessary repairs. Too much fuel Flooding a cold engine soaks the spark plug with raw fuel and, in more extreme cases, sends fuel dribbling out the carburetor air horn. Flooding can be induced by heroic cranking, but more often is the fault of the carburetor.

Float-type carburetors flood because of dirt between the inlet needle and seat or because of a hung float. Diaphragm carburetors are less prone to flooding, but will do so if the inlet needle sticks in the open position.

Flooding in a hot engine is more difficult to detect, since the fuel vaporizes. Sometimes you can see a curl of vapor leave the spark-plug port as the plug is removed.

In many cases, hot flooding comes about because of heroic cranking or because the choke was left engaged. If the problem persists when the engine has cooled down, assume that the carburetor is at fault. Lean mixtures Lean mixtures are a cause for alarm. The operator might notice flat spots during acceeration or that the engine runs better with a partially closed choke. A mechanic will see the bleached, bone-white spark plug insulator Fig.

In extreme cases, high combustion temperatures melt the piston crown. A white insulator tip is the first symptom of overheating, almost always caused by lean mixtures. Too much ignition advance on engines with adjustable timing has the same effect. The damage shown in the photo comes about when overheating results in detonation or preignition.

Bosch 44 Troubleshooting FIG. High combustion temperatures are death on pistons. This example exhibits pock marks left by metal fragments, deep scores, and, near the crown on the right of the photo, weld splotches. The engine is drowning in gasoline.

Unlike lean mixtures, gasoline-rich mixtures do no permanent damage, at least on engines without catalytic converters. It is also true that chronic misfiring darkens the spark plug. A replacement plug usually solves the problem. Compression Two-cycle engines develop two kinds of compression: crankcase and cylinder. Weak crankcase compression reveals itself as a refusal to ingest carburetor cleaner sprayed into the air intake. Some mechanics claim to be able to sense the crankcase pressure, which never amounts to more Tests 45 FIG.

Carburetors often vibrate loose from their mounts and leak air. The darker the color of the insulator, the richer the mixture. Bosch than 5 or 6 psi, as resistance on starter cord. The rest of us test crankcase integrity as described in Chap. Cylinder compression is another matter and should be checked whenever an engine enters the shop.

Vintage engines—West Bends, Clintons, Power Products, Villiers—could sometimes be persuaded to start with as little as 60 psi of cylinder pressure. Modern engines require 90 psi or more. Cylinder compression is a basic indication of engine health.

Robert Shelby Thread a compression gauge in the spark-plug port, open the throttle and choke, and crank three times Fig. If compression is a problem, remove the muffler and, using a soft probe, verify if the rings move in and out of their grooves.

Two-cycle rings are pegged to prevent rotation, but should move inward a few thousandths of an inch and spring back when pressure on them is relieved. Stuck or broken rings cannot seal. Now rotate the flywheel to bring the piston below the exhaust port.

Using a penlight, examine the far cylinder wall for scores. Any scoring costs compression. Raise the piston above the port. Scores, weld splotches, or extensive discoloration of the piston skirt are fatal Fig. Factory short blocks, that is, new rotating parts installed in new cylinder and crankcase castings, usually cost more than the engine is worth. When the engine spins freely without any resistance on the starter cord, we have zero compression. This condition can be caused by a holed piston or, as more often is the case, by a thrown rod Fig.

Repair is rarely worthwhile. The engine chokes on its own exhaust. Tests 47 FIG. What one hopes not to see when peering through the exhaust port. A parted rod, resulting from big-end bearing failure. Robert Shelby Lower the piston and, using a soft brass or copper tool, scrape the exhaust ports clean Fig.

Clear the cylinder of carbon fragments by spinning the flywheel rapidly with the spark plug removed. Chain saws and many garden tools incorporate a spark arrestor in the form of a screen over the exhaust ports or inside the muffler Fig.

Some Tecumseh engines have a compression-release port, which also requires cleaning. Clean the screen in solvent, being careful not to damage the fragile mesh. Torn screens should be replaced. Noncatalytic mufflers can be cleaned by immersion for an hour or so in hot water and caustic soda. Clogged catalytic converters must be replaced. Complaints Now that we have an appreciation of what engines require, complaints about engine behavior are not difficult to resolve.

Complaints 49 No start Failure to start with a new spark plug, fuel filter, and a quarter tank of fresh premix can have several causes, most of them obvious. We can pretty well forget about carburetor adjustments unless someone has jiggered with the carburetor since the engine ran last , carbonized exhaust ports, and other subtleties. No spark usually means a failed flywheel key, although the wire going to the kill switch should be checked for frayed insulation or burnt spots.

Crank the engine to determine if fuel gets into the cylinder. If the engine runs on aerosol, but not on gasoline, we can be confident that the problem is in the fuel system. Likely culprits are a dirty carburetor, hardened or leaking diaphragms, or a fuelpump malfunction. These and other fuel system malfunctions are detailed in Chap. And finally make a compression test, looking to find that magic psi number.

Reluctance to start That the engine starts at all means that compression and the ignition module are probably okay. But check the compression and, if you have not already done so, replace the spark plug with a known good one.

The most likely culprit is insufficient fuel, especially if the engine is of recent vintage. Clean and use whatever carburetor adjustments are available to richen the mixture. In some cases, the only recourse is to fit an earlier model, fully adjustable carburetor.

Runs a few minutes and quits Intermittent malfunctions are, almost without exception, confined to the ignition and fuel systems. Suspect a clogged fuel-tank vent Fig.