So how do these things work?
This section of cyclemaintenance.com will be dedicated to 4-cycle engines,
which covers most all of the street bikes out there that aren't dual
purpose. 2-cycle (or 2-stroke) owners, click HERE
for a message.
You need three things for an engine to run: FUEL, AIR, & SPARK
Just understanding this simple concept can help to significantly simplify
your troubleshooting efforts. Let's expand a bit.
- FUEL - usually in the form of gasoline. How does it
used? Let's pretend you are a molecule of gas. You start
out your journey from the gas tank, obviously. When the fuel tap
is set to "ON" and the engine isn't running, you just sit in
the tank. It takes a small vacuum to open the fuel tap so you
can flow into the carbs. Once the engine is started though, that
vacuum opens up the fuel tap. You then would flow through the
fuel tap (which sometimes can have a fine screen inside of it -
especially on older bikes). From the fuel tap, you likely head
into the fuel "rail" or fuel distribution pipe. This
varies from bike to bike, but usually goes to the very middle of the
carbs, and then branches out to each carb from there. After in
the fuel rail, you will travel to a carb (assuming the bike isn't fuel
injected). You flow from the rail into the carb, but only if the
float is down (the fuel level in the carb is lower). When the
float is down, it opens a "needle valve" that lets you flow
into the carb bowl. Think of the carb bowl as a second mini-fuel
tank. From there you will be sucked up into one of maybe three
different "jets" or nozzles. Inside the jet, you are
combined with a much larger volume of air and you will have to pass
the throttle (butterfly) valve and the carb piston. After you
are past there, it's on to the engine!
You head into the intake boot (which is usually rubber) and then wait
until your cylinder's intake valve(s) opens up. Once it opens
up, the piston will be moving down and will suck you with all that air
and a few other of your friends into the combustion chamber. The
intake valve closes behind you, the piston compresses you until it
gets to the top then....BANG - the spark plug fires. You convert
most of your stored energy into heat and pressure and force that
piston down. The exhaust valve(s) then open up, the piston
reverses again and blows you out to the header pipe. From there,
you head through some baffles and out the muffler/tail pipe.
- AIR - To come.
- SPARK - To come.
Can't wait for the rest of my explanation...try the HowStuffWorks
page on engines, which is a really good place to start.
Thanks for your patience!