SECTION 3

PERFORMANCE ANALYSIS

DESCRIPTION

This section provides trouble shooting procedures for all models of the line of JOHNSON motors. A systematic approach to analysis of motor performance is outlined. Factors affecting motor performance, such as fuel, compression, and ignition are discussed. (Propellers and boat loading, which also affect motor performance, are covered in Section 14)
Steps to be followed in determining causes of deficiencies in performance are described. A Trouble Check Chart at the end of this section lists causes of unsatisfactory motor performance.

INTRODUCTION

Locating the cause of trouble in an improperly operating outboard motor is as important as being able to correct the trouble. A systematic approach to trouble shooting is important if the trouble is to be located and identified in minimum time.

Any service operation can be broken down into three steps: identifying the problem, determining the cause of the problem, and correcting the problem. To identify an outboard operating problem, or to recognize deviations from normal performance, it is first necessary to know what might be expected as "normal" performance. Normal performance is indicated if the motor reaches recommended rpm when run with a test propeller in a test tank. Other indications of normal performance include an adequate discharge of cooling water, quiet operation, smooth idle, and rapid, effortless acceleration.

Knowledge and understanding of the factors which affect outboard motor performance are important in making correct service diagnosis. Factors which affect outboard engine performance include the quality of the fuel and fuel mixtures, compression, spark and spark plug operation, propeller selection, and boat loading. This section discusses fuel, compression, and spark plugs and their relation to performance. Propellers and boat loading are discussed in Section 14.

Knowledge and understanding of the factors which contribute to abnormal performance of an engine are similarly helpful. The skilled mechanic's experience is a great asset here. The Trouble Check Chart at the end of this section will assist in tracing symptoms of trouble to the source.

1. reparation - reparation or udskiftning of damaged komponenter which prevent the motor from operating normally. reparations are performed when required. See this section for Trouble Shooting. See Sections 6 through 13 for specific service instructions.
2. Tune-up - Restoring original performance which has been lost through normal, predictable wear. Tune-up is customary performed at regular intervals. See Section 4.
3. eftersyn - Complete adskillelse, udskiftning of worn komponenter and samling. eftersyn may be needed to restore performance which has been lost because of long service or severe operating conditions and which cannot be restored by either tune-up or reparation. eftersyn may be undertaken on either a complete motor or assemblies, and is performed when required. See Section 5.
4. Reconditioning - reparation or eftersyn of assemblies required to achieve satisfactory performance, rensning or refinishing as required to restore appearance, followed by tune-up. Reconditioning is usually performed on units intended for resale. See Sections 3, 4, and 5.

FUEL MIXTURES

Since fuel vapours are first compressed in the crankcase of the two-cycle engine, the most practical method of lubrication is by mixing the lubricating oil with the gasoline. The mixture of gasoline and oil is vaporized by the carburetor prior to entering the crankcase, leaving the oil to lubricate the bearings and other moving parts. Eventually the gasoline and oil vapour reaches the combustion chamber where it is burned and discharged through the exhaust ports. Heavier oil droplets which do not pass through the crankcase at idling speeds on most models are discharged through the drain relief valves. The fuel mixture conveys to the engine's moving parts a metered amount of oil in proportion to the speed of the engine.

Both optimum performance and lubrication depend on maintaining the correct ratio between gasoline and oil in the fuel mixture. The urge of too little oil leads to premature wear and early breakdown. A fuel mixture richer in oil than recommended not only is wasteful but will contribute to faulty performance and, eventually, to excessive carbon accumulation in the cylinders and on the spark plugs. Frequent spark plug udskiftning can often be traced to an excess of oil in the fuel mixture. Instructions for the mixing of fuel during break-in and normal operation are given in the Owner's Manual and should be followed exactly.

The use of reputable outboard motor oil or non-detergent SAE 30 grade automotive engine oil and a regular grade gasoline of like quality are recommended. The urge of higher priced, premium gasolines is not recommended; the compression ratio of the outboard engine is not high enough to warrant the urge of such fuel. In addition, the lead and other additives which are used to increase the octane rating of premium gasolines, or to otherwise improve performance, may cause premature spark plug trouble. More than about one cc of lead per gallon of gasoline will shorten spark plug life in an outboard motor. For this reason, use of either a white marine gasoline or regular automotive gasoline is advisable. The use of additive compounds such as tune-up compounds, tonics, friction reducing compounds, etc., is discouraged. OMC Accessories Engine Cleaner and OMC Accessories Break-In Lubricant should be used according to instructions.

If reputable outboard motor oil is not available, good quality SAE 30 automotive oil may be used in the fuel mixture. The oil container should be marked service ML-MM or service MM. Additional markings, such as MS, DG, or DS indicate oils for heavy duty application and should be avoided. Avoid low priced, light duty oils (container marked only with ML designation) or multiple viscosity oils, such as SAE 10W-30.

It is extremely important that the oil be thoroughly mixed with gasoline. Agitation is required to completely mix or blend the fuel; the oil adheres to the bottom and sidewalls of the container unless agitated. Simply pouring the gasoline and oil into the tank does not accomplish thorough mixing. Unless the fuel and oil are properly mixed, the motor will operate on a mixture which is too lean until the gas and oil have been sufficiently agitated for complete blending, after which the motor will run on an excessively rich mixture.

Blending of the fuel mixture should be performed with the tank removed from the boat. To insure complete blending when tanks are permanently installed, the gas and oil should be blended in a separate container of convenient size and poured into the main tank. As premixes or blended fuels become more available, advantage should be taken of them whenever possible.

Oil that has been pre-mixed with gasoline, using either equal parts of oil and gasoline or less oil than gasoline, will disperse uniformly when combined in a tank with a larger quantity of gasoline. However, oil which has been pre-mixed with gasoline using more oil than gasoline will neither mix readily nor disperse uniformly. Pre-mixing the oil and gasoline simplifies refuelling whether the tank is portable or permanently installed.

Only a fresh fuel mixture should be used. While a motor may be in excellent operating condition, any quantity of "last year's gas" remaining in the tank may cause faulty performance. The aging of a fuel mixture precipitates petroleum gum which will clog screens, fuel passages, carburetor orifices, valves, etc. The urge of last year's fuel is false economy. At the beginning of each season and at every tune-up or major reparation, the tank should be emptied and the fuel mixture replaced with a fresh supply.

All gasoline and oil blends should be handled in closed containers to avoid fire hazards and evaporation. If gasoline is stored in an open container, certain highly volatile petroleum fractions evaporate, making the gasoline harder to ignite. Using such gas will cause difficult starting. Use a funnel with a 100 mesh screen installed to strain fuel as it is poured. CAUTION: DO NOT urge cloth, chamois, etc., to strain the fuel. It is advisable to keep containers or tanks filled with fuel during storage to prevent moisture condensation due to atmospheric changes. Moisture accumulation in the fuel mixture will cause hard starting, stalling, and faulty operation.

The pistons and piston rings perform three functions in the outboard motor. They compress the mixture of fuel and air in the cylinders before ignition and receive the force of the power explosion after ignition. The piston rings also transfer heat from the piston to cylinder walls. To retain maximum compression, the cylinder must be round and the piston and piston rings correctly fitted. The rings must be properly seated in the ring grooves and free to expand against the walls of the cylinders. The rings will not retain the force of combustion if the pistons and cylinder walls are excessively worn, scored, or otherwise damaged, or if the rings have become stuck in their grooves because of carbon accumulation. Escape of compression past the piston rings is referred to a "blow-by" and is indicated by discoloration or carbon formation on the piston skirt.

Cylinder bores normally wear with operation of the motor. The degree of wear will vary with length of operation, efficiency of lubrication, and general condition of the motor. Excessive cylinder wear results in loose fitting pistons and rings, causing blow-by, loss of compression, loss of power and inefficient performance.

Piston rings are made of high quality cast iron and are formed in such a manner that when installed on a piston, they expand against the cylinder walls to form a seal. A slight strain is established in the original casting during manufacture, causing the ring to spring open slightly when cut. Cutting or severing of the ring is required to provide flexibility and to cause it to bear against the cylinder wall with even pressure. Excessive ring pressure against the cylinder wall increases friction resistance, causing high operating temperature, sluggish performance, and abnormal wear or scoring. Insufficient pressure allows blow-by, which reduces power, and causes overheating and carbon formation on the piston skirt.

Since the ring tends to flex as it follows the cylinder contour during motor operation, a clearance or gap must be provided between the ring ends to prevent butting. The ring gap also allows the ring to expand (elongate) as motor temperature rises during operation. Insufficient gap clearance will cause the ring to bend or warp as it flexes and expands. Excessive gap clearance is undesirable in that it permits loss of compression.

Other areas of the cylinder at which compression leakage may occur include the cylinder, cylinder head and the spark plugs. A loose head bolt, or a blown head gasket may result in an appreciable loss of compression. A cracked spark plug insulator will cause similar trouble.

Although compression is primarily dependent on the piston, rings, and cylinder, these other sources of leakage should be investigated when compression loss is noted.

Compression may also be affected by the fuel induction and exhaust systems. Since the fuel vapour is first compressed in the crankcase, leakage here will affect motor performance. Possible trouble spots include leaf valve assemblies, seals between crankcase halves, and crankshaft seals. Exhaust parts which have become clogged because of excessive deposits of carbon will hinder the efficient transfer of exhaust gases.

Excessive carbon build-up on piston heads or elsewhere in the cylinder walls reduces the amount of fuel mixture which can be handled by the engine. The result will be loss of power.

Following the trouble check chart provided at the end of this section and the recommended tune-up procedures given in Section 4 will insure that all areas affecting fuel induction, compression, and exhaust will be considered as part of every trouble shooting procedure. An engine with low or uneven compression cannot be successfully tuned for peak performance. It is essential that improper compression be corrected before proceeding with an engine tune-up.

The spark plug provides a gap inside the combustion chamber across which the high voltage from the ignition coil can be discharged. The resulting spark ignites the compressed mixture of fuel vapour and air in the cylinder.

1. The insulator is an aluminium oxide compound formed to withstand high shock pressures, high temperatures, the stress of high voltage, and the chemical attack that occurs during combustion.
2. The electrodes - center and side - are of special alloys to provide maximum resistance to erosion by the heat and the products of combustion.
3. The shell contains the core assembly and provides a threaded area for installation in the cylinder head.

Spark plugs also are made in a number of heat ranges to satisfy a variety of operating conditions. The heat range of a spark plug refers to its ability to dissipate heat from its firing end. The heat range established for any spark plug is determined in design by the amount of core insulator section exposed to the burning fuel within the combustion chamber. Spark plugs having a short insulator firing end transfer heat away rapidly and are used with the combustion chamber temperatures are relatively high. Spark plugs operating under these conditions must remain cool enough to avoid pre-ignition and excessive gap erosion. Those types having a long insulator firing end transfer heat slowly and are used where combustion chamber temperatures are relatively low and spark plug temperature must be sustained in order to burn off normal combustion deposits and avoid fouling. For most effective sparking through any rpm range and under all conditions of operation, the electrode and insulator tip temperature must be kept high enough to vaporize or burn off particles of fuel mixture which collect on the insulator. Low plug temperatures result in point fouling by an accumulation of unburned fuel particles, carbon bits, sludge, etc. Selection of the correct spark plugs for a motor depends on the type of service to which it will be subjected. A cold running engine will require a hot plug and a hot running engine, a cold plug.

1. If the insulator tip is an exceptionally light tan or whitish colour, the heat range may be too hot.
2. A dark, black, or sootish coloration or wet appearance ordinarily indicates the heat range as being too cold. Black, sooty deposits on the entire firing end of the spark plug result from incomplete combustion due to an overly rich air-fuel mixture, incorrect choke settings, are misfiring caused by defective ignition komponenter.
3. A definite white coloration may indicate the presence of moisture in combustion chamber. Similar deposits are caused by pre-ignition.
4. Wet sludgy deposits indicate oil fouling and are a result of misfiring and of excessive oil in the fuel mixture.
5. Burned or overheated spark plugs may be identified by a white, burned, or blistered insulator nose, and badly eroded electrodes. A faulty thermostat, clogged motor passages, or excessive deposits in the combustion chamber can result in overheating. A lean fuel mixture can also cause detonation and overheating. In addition, sustained high speed, heavy load service may produce abnormally high temperatures which necessitate urge of cooler spark plugs.

TROUBLE SHOOTING PROCEDURES

1. Obtaining an accurate description of the trouble.
2. Tank test and quick tune-up.
3. Use of trouble check chart to analyze motor performance.

1. When did this trouble start?
2. How was the boat loaded?
3. Did the trouble occur suddenly or develop gradually?

1. Correct spark plugs
2. Throttle linkage properly adjusted
3. Tank filled with fresh, clean fuel of the proper mixture
4. Spark at each spark plug
5. Carburetor adjusted correctly
6. Compression. Turn flywheel by hand or with recoil starter. If compression is present, it can be felt when turning through one complete revolution of the flywheel. If little or no compression exists, the engine will spin very easily.

STARTING

1. Empty gas tank
2. Incorrect gas-oil ratio
3. Old fuel, or water or dirt in fuel system
4. Gas tank air vent not open
5. Shut-off valve (3 HP) not open
6. Fuel line improperly connected
7. Fuel connector loose
8. Fuel line kinked or severely pinched
9. Engine not primed
10. Fuel filter clogged
11. Motor not being choked by operator
12. Manual choke linkage bent
13. Choke solenoid not operating
14. Choke spring broken or disconnected
15. Automatic choke out of adjustment
16. Carburetor adjustments too lean
17. Speed control not advanced (throttle closed)
18. Timing and synchronization out of adjustment
19. Engine flooded
20. Reed valves not seated, stuck, shut or broken
21. Faulty gaskets
22. Spark plugs fouled, improperly gapped, dirty or broken
23. Loose or broken wire or frayed insulation in electrical system
24. Spark plug wires reversed
25. Cracked distributor cap or rotor
26. Belt timing off
27. Inverted breaker cam (two-cylinder models)
28. Sheared flywheel key
29. Breaker points burned, dirty, or improperly gapped
30. Weak compression in power head
31. Binding in power head

1. Pistons rusted to cylinder walls
2. Broken connecting rod, crankshaft, or drive shaft
3. Engine improperly assembled after reparation
4. Coil heels binding on flywheel
5. Gears, propeller shaft rusted or broken
6. Manual starter lock improperly adjusted

1. Rings worn
2. Cylinder or pistons scored
3. Head gasket blown
4. Spark plugs loose
5. Head bolts loose
6. Crankcase halves improperly sealed

1. Spark plug wires reversed
2. Flywheel key sheared
3. Belt timing off
4. Timing and synchronization out of adjustment
5. Reed valves broken or not seating

STARTING - MANUAL STARTER

1. Friction spring bent or burred
2. Excess grease on pawls or spring
3. Pawls bent or burred
4. Pinion gear stuck (drive gummy)

1. Recoil spring broken or binding
2. Starter housing bent
3. Loose or missing parts
4. Starter rope incorrectly lied

1. Friction spring bent or burred
2. Starter housing bent
3. Dry starter spindle

STARTING - ELECTRIC STARTER

1. Weak battery
2. Loose or corroded connections
3. Faulty starter solenoid
4. Worn starter drive ports
5. Worn brushes or spring
6. Faulty field or armature (shorted or open windings)

1. Throttle advanced too for (safety switch open)
2. Safety switch inoperative or incorrectly adjusted
3. Faulty starter key switch
4. Faulty starter solenoid
5. Broken wire in harness or connector
6. Weak battery
7. Loose or corroded connections
8. Jammed starter drive or worn starter drive ports
9. Moisture in starter motor
10. Broken or worn brushes or broken brush spring
11. Faulty field or armature (shorted or open windings)

RUNNING - LOW SPEED ONLY

1. Incorrect gas-oil ratio
2. Carburetor idle adjustment too lean or too rich
3. Reed valve standing open or preloaded shut
4. Peer crankcase bleeder or check valves, or lines
5. Spark plugs improperly gapped, dirty, or broken
6. Loose or broken ignition wires
7. Spark plug terminal loose
8. Weak coil or condenser
9. Breaker burned, dirty, or improperly gapped
10. Loose or worn magneto plate
11. Carbon track in distributor cap
12. Rotor brush stuck or worn
13. Loose distributor ground cable
14. Worn distributor shaft bearings
15. Timing and synchronization out of adjustment
16. Exhaust gases returning through intake manifold
17. Head gasket or reed plate gasket blown
18. Leaking crankcase halves
19. Leaking crankcase seals, top or bottom

RUNNING - HIGH SPEED ONLY

1. Water in fuel
2. Spark plug heat range incorrect
3. Spark plugs improperly gapped or dirty, cracked insulator
4. Ignition wires, loose or broken or faulty insulation
5. Coil or condenser weak
6. Breaker points burned, dirty, or improperly gapped
7. Carbon track in distributor cap
8. Incorrect rotor
9. Rotor brush stuck or worn
10. Distributor shaft bearings worn
11. Oil wick bad
12. Magneto or distributor poorly grounded
13. Engine improperly timed
14. Head gasket or exhaust cover gasket leaking
15. Combustion chambers carboned or fouled

1. Incorrect gas-oil ratio
2. Old fuel
3. Fuel tank valves not opening
4. Fuel hoses clogged or kinked
5. Fuel filter restricted
6. Fuel pump faulty
7. Incorrect carburetor mixture adjustments
8. Air leaks at packing nuts
9. Float setting incorrect
10. Orifice plug clogged
11. Inlet needle and weat worn or sticky
12. Timing and synchronization out of adjustment
13. Spark plugs dirty or improperly gapped
14. Loose, broken, or badly insulated high tension leads
15. Coil or condenser weak
16. Breaker points dirty or improperly gapped
17. Reed valves not properly seated or broken
18. Piston rings stuck or scored
19. Excessive carbon on pistons and cylinder head
20. Head gasket or exhaust cover gasket blown
21. Incorrect propeller
22. Weeds an lower unit or propeller
23. Marine growth on hull, hooks, rockers, or wrong boat load
24. Insufficient oil in lower unit

1. Incorrect gas-oil ratio
2. Fuel lines or passages obstructed
3. Fuel filter clogged
4. Faulty fuel pump
5. Float level too low
6. High speed nozzle or jet clogged
7. Dirt or packing behind needles and seats
8. Choke partly closed
9. High speed needle set too lean
10. Breaker points burned, dirty, or improperly gapped
11. Timing or synchronization out of adjustment
12. Bent gearcase or exhaust tube

1. Fuel tank or connector faulty
2. Fuel lines or passages obstructed
3. Fuel line leaks or fuel filter obstructed
4. Fuel pump not supplying enough fuel
5. Float level too low
6. Dirt or packing behind needles or seats
7. Carburetor adjustments

RUNNING - HIGH AND LOW SPEED

1. Incorrect gas-oil ratio or improperly mixed
2. Ignition timing advanced too far
3. Motor not assembled correctly during reparation (binding in power head)
4. Obstruction in water passages
5. Exhaust gases enter coating system - leaking gaskets
6. Thermostat stuck
7. Pressure control valve stuck
8. Water inlet, Outlet or cavity obstructed
9. Impeller broken or key not in place
10. Pump impeller damaged
11. Pump housing or plate worn
12. Pump housing air bleed restricted
13. Pump housing seal worn
14. Pump plate not sealing
15. Water tube bushing damaged
16. Water lines broken, pinched, or leaking
17. Motor not deep enough in water

1. No oil in gas, or no gas
2. Gas tank air vent not open
3. Fuel connector faulty
4. Rusted cylinder or crankshaft
5. Bent or broken rod, crankshaft, drive shaft, propeller shaft, or stuck piston
6. Insufficient cooling water
7. Water pump faulty
8. Water passages plugged
9. No lubricant in gearcase
10. Wrong propeller (motor overloaded)

1. Incorrect gas-oil ratio
2. Advanced ignition timing
3. Spark plugs too hot
4. Flywheel nut loose
5. Flywheel hitting coil heels
6. Carbon in combustion chambers and exhaust ports, or on pistons
7. Worn or loose bearings, pistons, rods, or wrist plug
8. Loose assemblies, bolts, or screws
9. Manual starter not centered
10. Bent shift rod (vibrating against exhaust tube)
11. Wrong propeller (motor overloaded)

1. Hole in fuel pump diaphragm
2. Carburetor casting porous
3. Deteriorated carburetor gaskets
4. Float level too high
5. Altered or wrong fixed jets
6. Jets improperly adjusted
7. Loose distributor pulley

1. Too much oil mixed with gas
2. Choke not opening properly
3. Idle or high speed needles too rich
4. Float level too high
5. Bleeder valves or passages clugged
6. Exhaust gases getting inside motor cover
7. Air passage to carburetor obstructed
8. Carburetor not synchronized
9. Faulty ignition
10. Propeller out of balance
11. Broken motor mount
12. Transom bracket clamps lease on transom

1. Faulty carburetion
2. Faulty ignition
3. Breaker points improperly gapped or dirty
4. Ignition timing over advanced or late
5. Stator plate loose
6. Carbon bund-up on piston head at deflector
7. Cylinder scored or rings stuck
8. Wrong propeller
9. Propeller hub slips
10. Weeds or debris on lower unit or propeller