Fox engines have always been
a little on the noisy side, even with the recommended muffler
attached. With today's increased concerns over noise however,
it is desirable to keep the sound level as low as possible. Fox
does produce effective quiet muffler options for its Eagle, B
and C frame engines, but they tend to be a bit large and quite
heavy. We prefer to use this lightweight, effective, and very
Assembling the After-Muffler:
You can assemble your own effective
"after" muffler using a small aerosol shaving cream
can. This light weight addition to your stock Fox tilt up, or
tilt down, type muffler typically lowers the sound level by at
least 5db, and does not reduce power. On some engines, the maximum
rpm actually increases slightly! We have found that most
Fox engines run smoother, and seem "happier", with
the after-muffler installed.
The 50mL (travel size) can, produced
by Gillette, works well on engines from .25-.74, and weighs less
than 1oz. In addition, you will require some short lengths of
rubber hose to attach your after muffler and to provide an exhaust
outlet. We recommend automotive heater and/or fuel line hoses
because they are sturdy and provide proper support, particularly
at the inlet end that attaches to the stock muffler. (Silicone
tubing may be too flexible). Since these come in a variety of
sizes, you should have little trouble finding suitable diameters
for both inlet and exhaust ends.
The inlet hose, that attaches
the after muffler to the stock muffler, should have an inside
diameter that fits snugly over the "lip" on the end
of the stock Fox muffler. The exhaust exit hose should have an
inside diameter about the same as the stock exhaust outlet.
(It can actually be a bit smaller and still not reduce power,
while further lowering the sound level). Brass tubing and JB
weld could also be used to fashion the exhaust outlet, however
we have found that the rubber hose seems to have additional damping
qualities that take some of the "edge" off the exhaust
First, drain the can completely. Make
sure all the pressure has been released from the can or you will
likely be wearing the contents in step 2!
Now you must decide on the appearance you prefer. Unless you
wish your model to be a shaving cream advertisement, (perhaps
you are a Gillette employee?), you have two choices: Either remove
the existing finish to expose the natural aluminum, or paint.
If you choose to remove the existing finish, it is easier to
do it now before drilling holes in the can. Painting is the easiest
because the existing finish resists most solvents, so removal
generally requires a lot of elbow grease and wet sanding with
#400 sandpaper. Painting can be done after completion, but sand
lightly with #400 paper and clean thoroughly before application.
We have had pretty good luck with Coverite's 21st Century paint.
Pull off the spray nozzle, poke the remaining
stub into the can, then drill holes (approx. 3/8") in both
ends. If you prefer, the exhaust outlet hole may be located on
the side rather than the end. The inner workings can now be removed
and the empty shell washed out. Continue by using a round file
to open each hole to a diameter slightly smaller than the respective
inlet and exhaust hoses. You want the hoses to fit into the
holes very tightly!
Cut a length of hose for each end and
force (screw) it into the hole about 1/4". Trim the inlet
hose so that about 1/2" extends above the top of the can.
Trim the exhaust exit hose so that 1/2" extends beyond the
bottom of the can.
Fill in the cavity at the inlet end of
the can with high temperature RTV silicone to improve the seal
and provide some additional support. The cavity should be tightly
"packed" with silicone.
When the silicone has dried, slip the
after muffler over the end of the stock Fox muffler and secure
with a nylon zip tie. Since it is so light, no additional support
NOTE: It is very important
that the after muffler be installed as close to the end of the
stock muffler as possible. Do not increase the length of the
hose between the two! The engine will run hot and power will
When properly assembled and installed,
the after muffler will not reduce power or cause the engine to
overheat. On some engines the maximum rpm actually increases!
Engines with a two needle MK-X series carburetor may also show
an improvement in midrange performance.
After installation, you will
notice that the mixture is slightly richer. Readjust the needle
valve/s as required and the engine should perform normally.You
may also notice a more visible smoke stream in the air. This
does not necessarily mean that the engine is too rich. The after
muffler seems to act somewhat as a smoke system as well, particularly
if your fuel contains a significant amount of castor oil. Do
not attempt to run the engine overly lean to eliminate the smoke!
Adjust normally and just enjoy the show.