Re: Merc150 surges??
I have that same darn problem and it drives me crazy. Mercury 150 runs fine at speed, bring it back to idle and it sputters/dies. Let it cool and it runs fine. I can tell you what it is not: a)not oil injection system, mine removed and running 50:1 b)not spark plug wires c)not carbs, I just rebuild all 3 d)not old gas e)not air in fuel lines, I installed translucent Tygon 4040 lines f)not bad bulb b/c it's always firm g)not water pump, replaced recently h)not weak compression, have 120-130 lbs.<br /><br />I think I have it narrowed down to a residual gas/oil mixture in the throat of the carb after running at speed and possibly raising the motor in the shallows. Either that or maybe a weak poppet valve spring which would make the engine run too hot.<br /><br />I took off the sound box when it was surging and sputtering and there was some gas/oil mixture near the outside of the carb barrels (farthest from the reed valves, closest to the air box). I sprayed some carb cleaner on these little gas/oil puddles and the engine stopped surging and ran great. Now how do these little puddles get there? I don't know. The carb floats and needles are adjusted to 1/16" as the service manual recommends. Why is this little gas/oil puddle developing and not getting sucked into the motor at speed? I don't know but I am pretty sure this is the problem.
