Evening star., 1922-03-05
BACKF|R|NG CAUSED
BYLEAN MIXTURE
Expert Tells of Carburetor
Troubles and How to
Correct Them.
BY ALBERT N. ATKINSON.

How did your car take flre?" Il
don't know. I heard it pop back at
the carburetor and suddenly dis
covered that it was on fire." What
made 1t backf1re in the carburetor."
again I don't know. We can't find
out because the car Is total loss"
This is no imaginary conversation,
because cars have burned in the past
and will again In the future due to
backfring in the carburetor.
Fl The most frequent cause is lean
mixture. This means more air in the
mixture than usual. The carburetor
gets out of adjustment in some way
and the mischief is done. A mixture
Is slow-burning. 1t burns all during
the power stroke, all during the ex-
haust stroke, and it is still burning
when the inlet valve opens. admitting
the fresh mixture. This takes fire and
the flame runs back to the carburetor.
If there is any gasoline dripping from
the carburetor heavy vapor is form
ed, extending under the engine. where
1t is held by the mud pan. The fame
spreads under the engine and soon
nections and releasing a flood of
gasoline.
Lean mixture may be due to de-
rangement of the carburetor. or a
leaky inlet manifold. Spray noz1le
too far closed. auxiliary air valve
spring too weak or valve stuck open.
or clogged fuel line. are a few car
buretor causes. A leaky inlet mani
fold may be detected by running the
engine and injecting oil around the
joints. Oil will be sucked in at the
leak, where the bolts must be tight
ened or a new gasket installed in
place Of the leaky one.
We now come to troubles of the
I'll ,N.s@ H.
rare. The valve litter may be out of
adjustment, leaving no clearance. or
actually pushing the valve of it's seat.
If there Is little or no clearance the
valve will hold compression when the
engine is cold, but will leak when
the engine warns up, due to length
ening of valve stem. and, of course,
popping in the carburetor occurs i'm
mediately. Set the clearance at about
two thicknesseS of newspaper. Oc-
stuck. so that 1t cannot close: This
may be seen from the outside, as
there will be an unusually large space
between the valve stem and litter.
Electrical troubles now engage our
attention. With a single coil and dis
majority of cars. there would be
some distributor trouble or a short
circuit of the distributor wires. See
that all wires are properly insulated
ana wipe dll aust from
head. If you know how to open the
distributor you should wipe out the
inside occasionally, using cloth
dipped in gasoline. This will remove
all accumulations Of dust, which will
cause short circuit If allowed to re-
main.
Sh0rt-Circuit Troubles.
On a we'll known small car we find
the trouble caused by short circuits
or the timer wires. These chafe
against each other and sometimes
against the sides of the engine, wear
ing away the insulation and so caus-
ing troubles. Close switch using on
battery, or run engine on magnetic.
and advance and retard the spark,
watching the commutator and wires
If sparks are seen a short circuit is
indicated, which may easily be
stopped with tire tape.
Fortunately cars do not burn as
frequently now as they used to, prob
ably because the flame is led away
from the carburetor by the hot-air
pipe leading from the hot-air stove
on the exhaust manifold. But don't
think your car is safe on that ac-
count. There are leaks in these pipes
and there is an adjustment with
large holes to let in air when neces-
sary. So watch out for popping in
the carburetor and determine it's
cause Immediately. Here, as else
where. eternal vigilance is the price
Of safety"