Quote:
Originally Posted by J-Mech
Coop, a choke restricts air flow into the engine, thus making the fuel mixture more rich. Since the carb was plugged up and running lean, cutting the air entering the engine down, made the air to fuel mixture more accurate. It does not "suck" more gas into the engine with the choke on. Besides, if the jet is plugged, it couldn't get any more out of it anyway.
|
While I agree with that during cranking an engine Vs engining running at above idle. There are scientists smarter than you or I that will tell you while the engine is running a choked or partially choked carb will create enough vac to increase flow of fuel. If the jet is "plugged" your right. this may not be effective. However if there is a slight clog somewhere in a line the choke and vac could help pull fuel through into carb bowl.
I will look for the one theory I have read that says this can work as a venturi but the one I read most recently does describe it as "sucking" It also says it does this more easily when gas is introduced as a vapor.
The vacuum principles alluded to by Mr. Robin Parsons are, in greater detail, as follows: Bernoulli's principle states the faster a fluid is moving the more its internal pressure decreases. The faster a fluid is moving the less it is pushing back out on anything that might be exerting pressure on it. Choking may, incidently, cut down on the amount of air that gets into the cylinder, but restricting the amount of air is not the point of choking. What it does is to require the same amount of air to try to get into the cylinder through a smaller opening, because to do this the air must increase its speed. The now faster air has a great deal less internal pressure and, like all low pressure systems, it sucks vapor in from the higher pressure systems it is in contact with. It entrains things into its flow. In the situation under discussion gas vapor is entrained in an amount proportionatly higher to the increase in velocity of the "choked" airflow. Same amount of air, more or less, but a higher proportion of gas vapor, which, as Megashawn said, is more combustable, more prone to igniting, thereby boosting the engine up to smooth operating temperature.
Jon, In now way is this an argument.. I agree. Normal operation of a choke is to do just what you said. Cause rich condition to aid starting.