Originally Posted By: yaris0128
Choke literally means CHOKE the engine of oxygen. Its just to warm up the engine and get more fuel than air to the piston.
That's not "quite" correct (though it's close enough for England). Liquid fuel does not burn at the ignition point, vapor does. The carbs role is to vaporise the fuel (which is does pretty effectively under most conditions). In a cold engine, fuel tends to condense on the cold metal bits (intake tract, valve and anything else it comes in contact with). The chokes role is to make sure the mixture is rich enough that there is enough vapor there to burn. Raw fuel tends to wind up either as CO as it continues to burn with insufficient oxygen after TDC, or out the exhaust as raw fuel vapor. The chokes is there to ensure there is enough vapor to properly combust, but it ensures that occurs by putting more fuel than a warm engine would need down the intake.
Once the donk is warm enough, you can pretty much pour raw fuel down the intake in the right proportions and enough of it will vaporise on the hot metal to run right. Emissions is another story altogether of course, which is why we ended up with heated manifolds and all sorts of other complex gumph required to make carbs "good enough" at the time, but the general gist is the same.
The engine warms itself up whether the mixture is rich or not. In fact a rich engine generates less combustion heat and so in theory warms up slower (although the actual difference would be down in the noise). It just won't warm up if the vapor mix is so lean it won't run, thus the need for a choke.
