Evening star., 1924-09-07
No G.-Adiustinx the Carburetor.

A recent ride with Smith served to
clear up some points concerning the
carburetor. The discussion came
about as a result Of continued pop
ping back" while the engine was still
in process of warming up. This is
characteristic OF a cold engine, OF
course, but the power plant in Smiths
car was OVERRIDING it. When he in
formed me that the trouble was due
to Il leaky intake valve in the engine
demanded an explanation.
"A mechanic in the garage told me
So" Smith explained. The two valves
In each cylinder are supposed to be
tightly closed when the mixture is
fired. But if carbon prevents an in
take valve from seating properly
portion OF the burning mixture Will
pop back into the intake manifold
and carburetor. This same thing VIII
result from too tight an adjustment
of a push rod. Even a weak valve
spring would allow its valve TO re-
main open. 1t seems to me. therefore,
that we ought to go over these waive
tappetS carefully.
But | suggested that it would be
less work TO try adjusting the car
buretor for a richer mixture.
What makes you think there is
anything wrong with the carburetor.
Smith asked.
Popping back is due either to the
valves or the carburetor," | explained.
And I'm satisfied that it's the latter,
because if one of your intake valves
was not seating properly there would
be d loud clicking noise from the
valve compartment. But II you are
still in doubt let's drive. along until
the engine gets thoroughly warmed
IN and see what hapDenS.
Douhting the sense OF ii Smith
drove on and waited patiently for the
backfring. Much to his surprise 1t
became less frequent until finally ii
ceased altogether.
If the popping back had been
caused by d valve" said, the
trouble would increase as the engine
warmed up. because heat makes valve
stems expand and lengthen, thus in
creasing any tendency TO scat i'm
properly. You would also notice i
loss OF power and skipping of the en-
gine at both low and high speeds. But
when an engine is firing properly. yet
won't accelerate quickly or deliver
proper power on hills. there is usual
Iy something wrong with the carbure-
tor mixture. In hot weather we might
suspect overheatins and look TO the
fan or the cooling system. but not on
II itdt lItNt l4lIS. Aiio" SiiS tS 80
! and the chassis are we'll fabricated.
for ! saw YOU attend to all that yes
terday And your brakes are not
binding So there's nothing left but
the carOuretor.
And. anticipating that he was gong
to remind me that the instruction
books advise the owner to fuss with
the carburetor only as 4 last resort.
] added: "If you go at the work i'll
the right way. no harm can be done.
The trouble is that most car owners
change the adjustments too radically
and thus are unable to uote the mi
for better operation of the engine.
Some carburetors have one adjust
ment for air and one for gas: there
being no distinction between the
idiing and high speed requirements OF
! the engine other than the operation
OF an automatic high speed jet The
best adjustment tor this type is OBJ
tanned with the least amount of gas
and tho greatest amount of air, pro-
/ vided that the engine responds i'm
meGiateIy and does not pop back
when the throttle is suddenly opened.
with your type OF carburetor there
are no separate adjustments for air
! and gas. There is 4 distinction. how
ever. between idling and high speed,
with a separate adjustment for each.
This simplifies your problem because
you DO not have to take the idlin &
conditions into consideration. II the
idlinG mixture were too lean the en-