[alberg30] Re: A4 carb

[Gordon E. White]

Greg:
    I think you are on the right track with the carb adjustment.
Generally with a gasoline engine a coating of carbon in the tailpipe or
black smoke coming out indicates a rich mixture. I am not familiar
enough with the Atomic 4 to tell you how to adjust it, but that's
probably the solution. Is there a choke flapper that might be partially
closed? Or a restriction in the air cleaner?
    As to the plugs, they will carbon up if the mixture is stinking
rich, or if they are too cold, i.e. too short a path from the tip of the
insulator to the metal shell. I'd look at mixture first. After running
for a while your plugs ought to be dark tan; neither white (too hot) nor
black. They might be wet with fuel if you are severely rich, or oily,
from worn rings or valve guides. Light tan is ok, particularly with a
low-stress engine like the A-4.
    There was  a piece in the April 15th Practical Sailor on the A-4 as
used in  the Cal 34 relating that with no reduction gear the prop for a
sailboat with an A-4 should be 8" to 9" in diameter to get even close to
the 3,500 rpm necessary to see rated horsepower of the A-4. A prop that
small would only give 3 to 4 horsepower of thrust. CDI Props says the
"ideal" would be a 12" to 13" dia. prop of 6" pitch that allows the
engine to turn 1,700 to 2,000 RPM, giving about 14 horsepower of thrust.

    Since the Atomic 4 has a 1.3 - 1 reduction in reverse, you will need
more pitch in in reverse to get anywhere, so as a compromise CDI
recommends a 12 x 7 wheel.  I do not know this as a fact, but it seems
to jibe with my Atomic 4 experience in another boat of 34' length.
    So you are lugging the A-4 on an Alberg with a 12x7 wheel, which is
going to contribute to smoking.
                                        Gordon White A-275
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