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In article , says...

I have a 94' Chaparral with a 5.7 V8 Mercruiser. When starting the boat up
on the weekend after not starting up all week i get a blue/black smoke for
about 20 seconds then it dissapates. Also when starting it for the first
time i need to pop it in neutral and rev the rpms or else it will stall.
Any suggestions? ? ? Some have said since its an older boat/engine that is
nothign to worry about. Once it's running the smoke goes away and after
running a while i can start it right up w/o reving the rpms. Any info is
appreciated

-matt

This one is easy. The fuel in the carb is perculating down into the intake
manifold and into the cylinders who's valves happen to be open at rest. This
gas washes the oil off the cylinder walls. Presto!!! Next time you start it
up after having sat for several days, you get black smoke from the excess
fuel, and blue smoke from the oil which was fluidized off the cylinder walls.

This is common when the needle valves associated with the carb floats
allow fuel to seep past when the engine is shut down. When you turn the
engine off there is residual fuel pressure in the line, and sometimes
that excess fule ends up in the carb, and spills over into the intake
as described above.

Solution, have the carb rebuilt, or just live with it. Gas washing of
the cylinders will reduce the overall life of the engine, but I think it
would be hard to measure how little.