Mercury 35/40HP 2 Cylinder Outboards Service Manual PN 90-42794--1, Page 80Get this manual
CHECKING BLEED HOLE RESTRICTOR Check upper bleed hole (located inside transfer ports) to make sure that plastic restrictor is in holeIf this restrictor is missing, it will cause flooding-effect in upper cylinder and affect idle operationBLEED HOLE RESTRICTOR INSTALLATION If plastic restrictor is missing from upper bleed hole, install new restrictor as follows:
Pistons
Measuring Piston Roundness
Piston has tapered cam profile shape and is not true diameterUsing micrometer, measure dimensions "A,"S" and "C" at location shownDimensions should be as indicated in chart followingDimensions at Right Angle (90to Piston Pin
1Remove any burrs from hole opening2Use hammer and flat punch and tap new restrictor into hole3Retain restrictor by lightly peening over the hole opening in couple of places
Piston Measurements Piston Size Dim"A" DimB" Dim"C" CylBlock Finish Hone
Standard Piston
2.852" 2.867" 2.882"