1984-1986 Mercury Force 9.9 and 15HP Outboards Service Manual, Page 46Get this manual
UNBURNED FUEL IN NO.1 CYLINDER
UNBURNED FUEL IN NO.2 CYLINDER
4Note the reading on the gaugeA reading between 115125 p.s.i(9.915) indicates good compression If the reading is lower, there is compression leakFigure 4
Both cylinders should be within 10 p.s.iof each otherIf greater variation is experienced the cylinder head should be removed and an inspection made 10 find the problem (failed head gasketscored cylinderetc
AND lCTfO
INTO MD1 CYW'Ollil PIIIOIi TO Of.TOHATlON
Sometimes simply tig hten ing the head bolts to the proper torque wilt cure leaky head gasketFigure 2Fuel Tr.nlf.r Within Reclrcul.tlng g
TROUBLESHOOTING
Poor engine performance andor hard starting may be signs of compression problem Other signs include excessively smoky exhaust, badly fouled plugspower surging or extreme power lossAll can indicate engine co mpression problemsTherefore, when internal damage or wear is suspected as the cause of an eng ine problemcompression test hould be done firstComprlon Te.t: 1Remove both spark plugs from the powerhead2Insert the tip of the compression tester into the spark plug hole of the cylinder being tested Set throttle to wide open position Figure 33Crank the engine over with the recoil starter several times to make sure that each cylinder comes up forthe compression portion of its stroke