"You're pretty hard to please, Jim," his
wife observed. After all the fine weather we've had on this trip you growl
because we happen to run into a little rain in the last few miles! I'd say
we've had extra-good luck with the weather."
"Sure we have, dear," Jim smiled. "Don't
mind me. You know I always did hate driving in the - what the dickens has
They had stopped for a traffic light and,
Devon was talking the motor suddenly stalled. He
stepped on the starter again and again, but the motor refused to start.
Devon muttered, "never did that before. I guess one
of the spark plugs has gotten a soaking. Gimme the umbrella while I wipe
Holding the umbrella so that it protected
the motor as well as himself.
Devon carefully wiped the insulator of each spark
plug and the surface of the cable leading to it. When he climbed back into
the car and stepped on the starter pedal again the motor started at once.
Guess I know my onions!" he bragged, as
they started down the road.
"Now, as I was saying - " He did not
finish the remark, for the motor interrupted it by going dead again.
"Now what in thunder is the
Devon exclaimed. "Can't be the spark plugs this
time, because it's almost stopped raining. Maybe there's a loose wire
He got out a screwdriver and pliers and
tested all the wire connections he could get at conveniently, but found
"Humph!" he grunted. "Must be a
burned-out coil or something. Well, guess I'd better phone the Model Garage
and have Gus tow us the rest of the way home - it's only three miles or so."
"First try it again. Maybe it'll work
now," his wife suggested.
Devon followed her advice and the motor started at
once. However, it skipped explosions and showed signs of stalling again at
slow speed so that he had to keep his foot on the throttle all the time in
"Take me home first, so I can get dinner
started," his wife suggested, as they came in sight of the Model Garage,
"and then you can run back and have it fixed while the meat is cooking."
"O.K. by me, if it'll run that far,"
Ten minutes later, he pulled up in front
of the Model Garage with the motor racing. As Gus Wilson, mechanic and half
owner of the establishment, came over to him, he took his foot off the
throttle pedal and the motor stalled almost at once.
"That makes the third time it's gone to
sleep like that in the last half hour, Gus. See if you can find what's the
As Gus lifted the hood, the odor of raw
gasoline filled the air. The outside of the carburetor was dripping with
"Shouldn't be hard to find that trouble,"
Gus muttered. "The motor is being drowned in gasoline. Either the
carburetor float has sprung a leak there's dirt under the float needle valve
or it's a combination of a tiny bit of dirt under the float needle plus too
high fuel-pump pressure."
"And I thought it was rain on the spark
Devon growled, crestfallen.
"No ordinary rain ever stopped a motor
once it was warmed up well, Gus maintained, "unless the distributor cap
leaked water or was cracked or something like that. Of course, in the kind
of a rainstorm we've just had enough water may be blown through the radiator
or sideways through the hood louvers to make one or two of the spark plugs
skip a few explosions, but the heat of the engine at normal running
temperature will evaporate any water that hits them in no time at all.
"No," continued Gus, as he got his tool
kit and started to remove the carburetor, "about the only time rain
puts the ignition out of kilter is when
you leave the car in the rain for hours till it is stone-cold and a film of
moisture settles all over the plug insulation and the high-tension wiring as
Sometimes the motor won't start under
such conditions, and even if it does the wettest plugs are likely to miss a
lot till the motor warms up enough to dry off the moisture."
"Anything the matter with that float?"
Devon asked, as Gus removed it from the carburetor
and shook it gently.
"Tight as a drum," Gus replied. "If any
gas had leaked into it, you could hear it slopping around when you shake
it. There doesn't seem to be much dirt in the carburetor either, so I guess
we'd better have a look at that fuel pump."
Gus disconnected the gas pipe between the
fuel pump and the carburetor, and connected the former with the gauge on the
testing stand. Then he started the motor, which could be run for a brief
time on the gasoline remaining in the carburetor float chamber. The gauge
showed that the pressure developed by the pump was considerably higher than
it was supposed to be.
"Now, here is what happens," Gus
explained. "So long as no dirt gets under this needle valve that is
operated by the rising and failing of the float everything is fine, because
the extra pressure is not nearly enough to force the needle open against the
closing pressure produced by the float. But the minute the tiniest speck of
dirt lodges under the needle, the gas keeps on flowing after the gasoline
level in the float chamber has reached its proper height.
"Of course, the speed of this excess
flow," Gus went on, "depends on how big the speck of dirt is, as well as on
the pressure of gasoline. And you've got to remember that the motor, even
when it's idling, uses gas steadily. If the fuel-pump pressure is normal, a
tiny piece of dirt under the needle will not cause gas to flow faster than
it is burned by the engine, so no harm is done."
"Now I get it,"
"If the pump pressure is high, a lot more
gas is forced through, the carburetor is flooded and the motor stops from
having too rich a mixture. So when I let the motor stand while I cleaned
the plugs the first time it started, and while I tried to find a loose wire
the second time the excess gas cleared away and the motor started. And I
was blaming the ignition all the time!"
Gus smiled. "Anybody could make that
mistake. The funny part of it is that you probably could have started the
motor right away either time just by opening the dash control of the
throttle and holding it that way for a few seconds before you stepped on the
starter instead of giving the throttle pedal a quick jab like most people do
at the instant when they step on the starter.
"When you jab the pedal," Gus explained,
"this plunger shoots raw gas into the manifold - because there's too much
"So what I should remember,"
Devon summed up, "is that the next time the motor
stops like that, I should get it started with the dash-control throttle and
of course, not use the choke. Is that right?"
"Correct - if the dirt that's causing the
trouble happens to be under the float needle valve," Gus pointed out. "But
if the motor stops when it's idling because dirt has partly clogged the
carburetor jets, then you're up against exactly the opposite situation. In
that case, the motor dies from gas starvation, so pulling out the choke to
get a thicker mixture in the cylinders will get you started. And, after the
motor is idling pretty fast, you often can suck the dirt out of the clogged
jet by yanking the choke all the way out for a half second or so while you
step on the throttle. That trick also will cure 'stuttering' caused by
water in the carburetor."
"That makes sense,"
Devon agreed, "but how do you know which trouble
you're up against? Suppose she just stalls. How are you going to tell
whether it's dirt under the float needle or dirt in the idler jet?"
"Since it usually happens in traffic,"
Gus replied, "and the first thing you notice is that the motor isn't running
any more the best thing to do is to treat the motor as if it were flooded -
and if it doesn't start after a couple of attempts, then give it the works
with the choke. Always try the remedies in that order, because if you go at
it the other way around, you'll flood the motor worse than ever - if
flooding happens to be the trouble."
"Of course," Gus added, "if the trouble
is caused by a leaky float that lets the level of gasoline in the float
chamber get too high, the way to get the motor going when it stalls from
flooding is the same as for dirt under the float needle. But unless you
have the float fixed at the first opportunity, it'll only be a question of
time before enough gas gets inside the float to sink it, and then your goose
will be cooked. The motor will choke up every time you start it, and you
won't be able to keep the engine running at all except at racing speed."
"Seems to me,"
Devon recalled, "I had a leaky float on a car I owned
several years ago, and while the motor ran pretty badly, stalled often, and
used a whale of a lot of gasoline. I could still use it, and it certainly
didn't stall every time I started the motor. Why shouldn't a modern car do
at least as well?"
"Your old car," Gus explained, as he
finished the job on the carburetor and fuel pump, "undoubtedly had a
vacuum-tank fuel feed that probably was set pretty close to the level of the
carburetor. Besides that, I doubt if the float could have been so filled
with gasoline that it wouldn't float at all. Anyway, it wouldn't have
worked that well with a modern pump-feed system, if the pressure was higher
"Couldn't the old vacuum tank produce
extra pressure too?"
"That was one of the faults it didn't
have," Gus chuckled, "although it had plenty of others.
"With a vacuum tank, you know, there was
no pressure-feed system like you have with a fuel pump. The gas just
flowed down from the tank to the carburetor by its own weight.
"It's easy to see that when you get your
pressure by letting gasoline flow down by gravity from one tank to another,
the only way you could get higher pressure without moving the vacuum tank
would be by changing the law of gravity - and even Einstein hasn't been able
to do that!"