Suzuki outboard motors 1988 2003 repair manual., Page 244Get this manual
7-32 POWERHEAD SECONDARY COMPRESSION TEST
Anything that generates heat andor friction will eventually burn or wear out (for example, light bulb generates heat, therefore its life span is limited)With this in mind, running powerhead generates tremendous amounts of both; friction is encountered by the moving and rotating parts inside the powerhead and heat is created by friction and combustion of the fuelHowever, the powerhead has systems designed to help reduce the effects of heat and friction and provide added longevityThe oil injection system combines oil with the fuel to reduce the amount of friction encountered by the moving parts inside the powerhead, while the cooling system reduces heat created by friction and combustionIf either system is not maintained, break-down will be inevitableTherefore, you can see how regular maintenance can affect the service life of your powerheadThere are number of methods for evaluating the condition of your powerheadA secondary compression test can reveal the condition of your pistons, piston rings, cylinder bores and head gasket()A primary compression test can determine the condition of all engine seals and gasketsBecause the 2-stroke powerhead is pump, the crankcase must be sealed against pressure created on the down stroke of the piston and vacuum created when the piston moves toward top dead centerIf there are air leaks into the crankcase, insufficient fuel will be brought into the crankcase and into the cylinder for normal combustion See Figure 13
The actual pressure measured during secondary compression test is not as important as the variation from cylinder to cylinderOn multi-cylinder powerheads, variation of 15 psi or more is considered questionableOn single cylinder powerheads, drop of 15 psi from the normal compression pressure you established when it was new is cause for concern (you did do compression test on it when it was new, didn't you?) If the powerhead been in storage for an extended period, the piston rings may have relaxedThis will often lead to initially low and misleading readingsAlways run an engine to operating temperature to ensure that the reading you get is accurate1Disable the ignition system by removing the lanyard clipIf you do not have lanyard, take wire jumper lead and connect one end to good engine ground and the other end to the metal connector inside the spark plug boot, using one jumper for each plug wireNever simply disconnect all the plug wiresPRIMARY COMPRESSION TEST
Because the 2-stroke powerhead is pump, the crankcase must be sealed against pressure created on the down stroke of the piston and vacuum created when the piston moves toward top dead centerIf there are air leaks into the crankcase, insufficient fuel will be brought into the crankcase and into the cylinder for normal combustion If it is very small leak, the powerhead will run poorly, because the fuel mixture will be lean and cylinder temperatures will be hotter than normalRemoving all the spark plugs and cranking over the powerhead can lead to an explosion if raw fuelloil sprays out of the plug holesA plug wire could spark and ignite this mix outside of the combustion chamber if it isn't orounded to the enaine p