THE SECRET WORLD OF CARBS
by Paul Bryant, Viking Exhaust
The basic secret of carb function is that inside each carb are thousands of
tiny gnomes; each with a small bucket. As you open the throttle, more of these
gnomes are allowed out of their house and into the float bowl, where they fill
the buckets and climb up the carb's passages to the intake, where they empty
their buckets into the air stream. But, if you don't ride the bike for a while, bad things can happen.
Tiny bats take up residence in the chambers of the carb, and before long the
passages are plugged up with guano. This creates a gnome traffic jam, and so
not enough bucketfuls of fuel can get to the engine. If it gets bad enough,
the gnomes simply give up and go take a nap. The engine won't run at all at
this point. Sometimes you'll have a single dedicated gnome still on the job,
which is why the bike will occasionally fire as the gnome tosses his lone
bucket load down the intake.
There has been some research into using tiny dwarves in modern carbs. The
advantage is that unlike gnomes, dwarves are miners and can often re-open a
clogged passage. Unfortunately, dwarves have a natural fear of earthquakes, as
any miner should. In recent tests, the engine vibrations caused the dwarves to
evacuate the Harley Davidson test vehicle and make a beeline for the nearest
BMW dealership. Sadly, BMW's are fuel injected and so the poor dwarves met an
unfortunate end in the rollers of a Bosch fuel pump.
Other carb problems can also occur. If the level of fuel in the float bowl
rises too high, it will wipe out the poorer gnome housing in the lower parts
of the carb. The more affluent gnomes build their homes in the diaphragm
chamber, and so are unaffected. This is why the bike is said to be "running
If the fuel bowl level drops, then the gnomes have to walk farther to get a
bucketful of fuel. This means less fuel gets to the engine. Because the gnomes
get quite a workout from this additional distance, this condition is known
as "running lean".
The use of the device known only as the 'choke' has finally been banned by PETG
(People for the Ethical Treatment of Gnomes) and replaced by a new carb
circuit that simply allows more gnomes to carry fuel at once when the engine
needs to start or warm up. In the interests of decorum, I prefer not to
explain how the 'choke' operated. You would rather not know anyway.
So, that's how a carburetor works.
-From "Setting Up Amal Carburetors", Norton News (Spring, 2005). International
Norton Owners Association (www.inoanorton.com)