Basics of Carburettor Operation

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 houses 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 Section 8 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 rich". 

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 carburettor works. You may wish to join us here next week for electricity 101, or "How your bike creates cold fusion inside the stator, and why the government doesn't want you to know about it."