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MORRIS CARS.
A Correspondent's Queries.
'W.G.',_ Northam, asks for advice on
the following points in connection with a
Morris car.
(1) Should, the engine pick up speed 'when
rubber tube (which is connected to the wind
screen wiper) is removed from the induction
pipe, even when engine is cold . and with car
buretter control' at ?weak, magneto control at
advance?.' I have noticed 'this, happen several
times in the garage. '- '-
(2) Will you explain why the jet settings
of 16-21-15-12 on Smith carburetter should give
a better mileage than those fitted in the first in
stance, .viz.. 17-20-17-10, as I understand that
these figures represent the amount of petrol in
cubic centimetres tliat will pass through these
jets in a given time, and when added together
come to the same total? I understand that the
former settings are advised for engines that have
been properly run in. The car has done 10.000
miles.
(3) In the event of very bad starting from
cold, even when engine has been cranked tho
roughly free by hand, would you suspect the
magneto as being the cause of the trouble,
inasmuch as this may require re-magnetising,
everythinjr else apparently being in order.
The answers are as follow: —
(1) If the engine accelerates -when the
tube to the windscreen wiper is taken off the
carburetter, the mixture passing to the -engine
at that particular moment is too rich. It does
not follow, however, that the mixture J3 too
rich ithroughout the throttle ranged asa- slight
richness at small throttle openings is advan
tageous in order to obtain rapid and smooth ac
celeration then the throttle is suddenly opened.
(2) Thr-re are many reasons why a jet set
ting of 16-21-15-12 should give a better pet
rol consumption than a setting of 17-20-17-10,
but it is hardly a matter that can l-e discussed
fully in these columns. In short, however, al
thuugh the total capacity of the two jet ar
rangements is the same, the total of the first
three jets, namely 'those which' are responsible
for carburation over the normal 'touring speed
range, is less in the case of the alternative jet
setting. An economy is therefore effected. A
comparatively large jet is fitted in the second
jet position, and since a rich mixture is re
quired for rapid acceleration, the acceleration
,-will be improved with the -alternative jet ar-,
Tangement without affecting ' the petrol con
sumption adversely! On the contrary, the bet
ter acceleration obtained with the alternative set
ting recommended gives greater economy, for
the' throttle opening required to attain a cer
tain speed in a fixed length of time is not so
great.
(S) There arc many causes of difficult start
ing, an irregularity in the working of the mag
neto being one of the most' remote. Choked jets
will cause difficult starting, as will faulty blow
running jet adjustment. An error in the set
ting of the mixture control sleeve will also
make starting difficult, more particularly if the
sleeve does' not completely cover the first and
second jet choke passages. Although the spark
ing plugs may be perfectly dry and clean, start
ing troubles will be experienced if the sparking
plug points are not set accurately, a difference
of .002in. being all-important. Wherea3 diffi.
cult starting- may be experienced with a plug
point setting of .020in., no trouble will be ex
perienced if the gap is reduced to .01 Sin. Faulty
ignition timing will also have a distinct bear
ing on easy starting, and if difficulty is experi
enced tha setting of the magneto should al
ways be carefully checked. Tappet clearances
should also be checked in order to make sure
that the valves are seating properly. Leakage
of gas past the valves will cause loss of com
pression as well as mixture dilution, and this
in turn will make starting difficult. One or more
of the valves may also be badly pitted or dis
torted,. in which case persistent bad starting will
continue until these have been rectified. It should
be noted that different brands of petrol have a
certain effect on ease of starting.
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