1986+ Mercury 6/8/9.9/10/15HP 2-stroke Factory Service Manual, Page 130Get this manual
FUEL DELIVERY SYSTEM
Problem: Fuel Blowback Out of Carburetor Problem: Unable to Reduce Engine RPM to Slow Idle Possible Cause Chipped or broken reeds on reed blockProblem: Rough Idle Possible Cause Excessive preload on reedsProblem: Engine Runs Too Lean Possible Cause Carburetor is looseAir leaks past mixing chamber coverFuel level is too lowClogged high speed jetRestricted fuel flow to carburetorIncorrect high speed jetIdle mixture set too leanAir leakage into fuel systemCorrective Action Tighten bolts securelyTighten cover or replace gasketReset float levelInspect jet for varnish or debris and cleanCheck fuel lines and filters for restricted flowRefer to main jet chart and replace with proper jetAdjust to run richerTurn idle mix screw counterclockwiseInspect fuel line connections, hose clamps, fuel pump and fuel outlet tube (located in fuel tank) for loose fittingsInspect valve andor test engine without valve in fuel systemReplace reedsCorrective Action Replace reedsCorrective Action