Motor Carburetor Rebuilding
By FLC & WCCB member Dick Newcomb
Carburetor rebuilding on a typical outboard is not
too bad an undertaking especially with a couple of
handy helpers. One is a digital camera. Take a zillion
pictures as you're removing things to get the carburetor
off and as you take it apart. Photographing any disassembly
is essential, especially if you've not done it before.
Pictures will be invaluable when you go to put things
back together, typically days or even weeks later.
The second helper is to invest in one of the Seloc
(or other company's) books for that type of motor.
They usually are printed by model, for a range of
years (such as "prior to 1965" or "1965-1976"),
and also by ranges of horsepower (like 3hp-40hp).
Most of these are well-written and take you step-by-step
through the disassembly and reassembly processes.
They can be a bit like tackling a foreign language
when you first start, so it is helpful to enlist the
assistance of club members who have done this sort
of thing before. Sharing information like this is
one of the main reasons our ACBS family exists.
you have removed the carburetor, it can usually be
opened up by removing five screws that hold the two
halves together (see pictures 1 and 2). Slowly crack
it open and gently pull the two halves apart. Use
a small container like an old cottage-cheese container
to hold all the parts. Remember to keep taking those
pictures! You will find a cork structure in a ring
shape inside. This is the float. It sits inside the
bowl where gas enters the carburetor. As gas comes
in, it "floats" up and actuates a small
needle valve. Once full it is supposed to push that
valve up and shut off the gas. Stuck floats can be
a major cause of engine trouble: stuck down, they
allow the carburetor to flood; stuck up, no gas can
get in. The float should be about parallel as you
hold the carburetor level. If not, use a small pair
of needle-nose pliers and gently bend the brass hinge
until it is level.
Examine the general condition of the inside of the
carburetor. If everything is nice and clean you may
have lucked-out and won't need to tear things apart
too much. Here is where an air compressor really helps.
If you have one , use the fine air spray tip and blow
air through every hole you can find. Take the two
jets out. Low or idle speed is typically at the top
of the carburetor; high speed is at the bottom. Unscrew
them, remove them and look things over (picture 3).
A good slow-speed jet is a sharp needle-like point.
This is where most problems with idle occur. If the
motor runs but won't idle down, bucks, misfires and
stalls, it is probably a bad slow-speed needle. If
you have any doubt, buy a new one. I've rarely seen
a problem with the high-speed jets. They are blunt
on the ends. There may be dirt or varnish build up
on the needle, but they don't generally go bad.
With the high and low needles out, blow out all the
openings. If everything blows through you, may be
able to reassemble your carburetor and try it, which
is the only way to know if it will function properly
Let's assume the worst. You open up the carburetor
and it is a gummy mess! Now you need to remove everything
you can take apart (take pictures). You then need
to soak all gummed-up pieces in a good carburetor
cleaner for several days. (The cleaner is nasty stuff
so put it in a closed container.) You also need to
invest in a rebuild kit available at NAPA, through
a marine supplier, or any of the Outboard Club web
Once you've cleaned all those little parts, rebuild
the carburetor with the new gaskets, etc. from the
kit. You won't need everything, but the gaskets, float
needle and new seals for the needle valves are critical.
Well, put her back together and cross your fingers!
Start by turning the needle valves -- low and high
-- all the way in. Now open them about 1¼ turns.
Try your motor, if it fires and runs in a barrel of
water, you're in good shape. But the only way to get
it adjusted is out on the lake.
Start with high speed. Open her up and adjust the
needle in and out until you get the top end speed,
then turn it in just a little. Next, go to idle speed
and do the same. Most older outboards (other than
the little kickers) weren't super-designed for slow
speed. What do you normally do when you take a boat
out? Start up, coast a little ways and then open it
up once you're in deeper water. Most motors over 25hp
aren't idled much.
Well, good luck. I'd be glad to help anyone with their
Next time: Coils and points.