Re: 1995 150 Black Max
I have a 1996 Mercury 150HP carbed motor. I had a similar problem until I did the following based upon advice of a Merc service mechanic and recommendations from others in this forum.
1) I replaced the two check valves on the oil injection system. One is located between the hose going to the remote oil tank and power head just below the starter. The other one is located between the oil pump and the fuel pump. If either of these check valves are defective, it can cause excess oil to be pushed into the fuel stream after shut down causing excess smoke at the next startup. (There are various threads on this subject).
2) I tilt the motor up a little before I shut down. At least, I don't have it tilted down so far that any fuel sitting in the cab barrel at shut down could run backwards into the engine. Apparently a little fuel can enter the carb barrel after shutdown and it is better if it flows forward out of the carbs rather than backwards into the motor.
I did both so I can't be sure which of these two fixes had the most effect in solving my problem (or if both were necessary) but at least I cut down a lot on my smoke at startup issue.
Other recommendations I had gotten is to clean the carbs, checK that the carb floats are correctly adjusted, and to change to a synthetic oil. I didn't do any of these because my smoke problem was limited to startup, rather than when idling continuously, so I figured that these were not probable solutions to my problem. This may not apply to your smoke problem or perhaps I just got lucky that the solutions I chose fixed my problem.
Good luck
