Suzuki outboard motors 1988 2003 repair manual., Page 65Get this manual
FUEL SYSTEM 4-3 Alcohol in fuel is either methanol (wood alcohol) or ethanol (grain alcohol)Either type can have serious effects when applied to outboard motor applicationsThe leaching affect of alcohol will, in time, cause fuel lines and plastic components to become brittle to the point of crackingUnless replaced, these cracked lines could leak fuel, increasing the potential for hazardous situations uSuzuki fuel lines and plastic fuel system components have been specially formulated to resist alcohol leaching effectsFACTORS AFFECTING COMBUSTION
The combustion process is affected by several interrelated factorsThis means that when one factor is changed, the other factors also must be changed to maintain the same controlled burn and level of combustion stability Compression
When gasohol becomes contaminated with water, the water combines with the alcohol then settles to the bottomThis leaves the gasoline and the oil for models using premix, on top layerWith alcohol-blended fuels, the amount of water necessary for this phase separation to occur is 0.5 by volumeAll fuels have chemical compounds added to reduce the tendency towards phase separationIf phase separation occurs, however, there is possibility of lean oillfuel mixture with the potential for engine damageWith oil-injected outboards (Precision Blend models), phase separation will be less of problem because the oil is injected separately rather than being premixedDetermines the level of heat buildup in the cylinder when the air-fuel mixture is compressedAs compression increases, so does the potential for heat buildup Ignition Timing
Determines when the gasses will start to expand in relation to the motion of the pistonIf the gasses begin to expand too soon, such as they would during pre-ignition or in an overly advanced ignition timing, the motion of the piston opposes the expansion of the gasses, resulting in extremely high combustion chamber pressures and heatAs ignition timing is retarded, the burn occurs later in relation to piston positionThis means that the piston has less distance to travel under power to the bottom of the cylinder, resulting in less usable power Fuel Mixture
two cycle engine has power stroke every revolution of the crankshaft four cycle engine has power stroke every other revolution of the crankshaft Therefore, the two cycle engine has twice as many power strokes for any given RPM If the displacement of the two types of engines is identical, then the two cycle engine has to dissipate twice as much heat as the four cycle engine In such high heat environment, the fuel must be very stable to avoid detonation If any parameters affecting combustion change suddenly (the engine runs lean for example), uncontrolled heat buildup occurs very rapidly in two cycle engine
Determines how efficient the bum will beA rich mixture burns slower than lean oneIf the mixture is too lean, it can't become explosiveThe slower the burn, the cooler the combustion chamber, because pressure buildup is gradual Fuel Quality (Octane Rating)