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No this is not as stupid as it sounds. What I mean is, how does the throttle make the engine spin faster? (or slower)

The throttle valve allows more air to enter the engine. The carburetor adds fuel proportional to the amount of air flowing into the engine. More air/fuel mixure = more energy, which can allow a higher RPM.

to expand a bit on that. The more power is cause by a bigger boom. And the bigger boom (while meaning more power) also pushes the cylinder faster, which turns the crank, which means the cams and CDI (in my case) spin faster as well, which means the spark plugs fire faster, the air/fuel mixture is sprayed in faster, and the exhaust is kicked out faster.

You turn the throttle, the more you turn the throttle, the more a valve opens in the carb (if it's carburated). The more the valve opens, the more air is able to flow through the carb. The more air through the carb, the more gas that is mixed with it. So, the combustion chambers are getting more air/fuel mixture, which creates a larger explosion. Larger explosion=more power. More power=higher rpms. Higher rpms=faster speed.

Of course, then you through in different gears, so that changes the torque:speed ratio. But the first explanation simplifies it.

wow! i always just thought there was a little hampster on a wheel in there, and when you twist the throttle it dropped a carrot closer to its nose so it would run faster.

i think we all learned something today.

Twist it...duh!!!

HandsomeRyan wrote:wow! i always just thought there was a little hampster on a wheel in there, and when you twist the throttle it dropped a carrot closer to its nose so it would run faster.

i think we all learned something today.

cool. thanks.

So how does the engine braking work? Wouldn't the crankshaft continue to spin just by inertia?

Pumping losses mostly.

The engine is like a big air compressor. It pulls air in, compresses it, then pumps it out the exhaust. All of that takes energy which is normally supplied by the fuel. Remove the fuel and the engine starts absorbing power instead of supplying it.

A lot of those losses come from Adiabatic Heating....Simplified: if you take a gas (e.g. air) and compress it, it gets hot. That's how diesel engines work... the air in the cylinder gets so hot from being compressed as the piston goes up that the diesel fuel (when injected) catches fire...well, if there is no fuel, that heat soaks into the cylinder walls and radiates out through the cooling fins or is carried away by the coolant. Another large percentage (perhaps larger than adiabatic...can't recall) comes from the air resistance of pulling air through the intake, through the cylinders, and out of the exhaust...sort of like the effort required to blow the water out of a garden hose.

And then of course there is just the mechanical effort needed to move the engine...pumping oil, generating electricity, and such all takes energy which must come from somewhere.

interesting. When I engine-brake my bike it starts farting. Is this normal? What causes it?