choke only cold engines?
 

After all these years of driving IC gasoline engines, I still do not fully understand why, under normal circumstances, a cold engine must be "chocked" to start.
Would someone please explain to me why this is necessary?
Gracias,
Phil

Re: choke only cold engines?
 

You should limit the use of the choke to a minimum. Too much choke can foul the plugs and/or flood the engine. The choke blocks off the top of the carburetor and exposes the jets to manifold vacuum meaning more fuel and less air. The first 1/2" also opens the throttle a fraction too. Sometimes just pulling out about 1/2" is enough to allow it to idle just a little bit higher. If it is the first start on a cold day you may have to pull it out 75% or more, but start easing it in as soon as it start running.

Re: choke only cold engines?
 

Chocking restricts the flow of air into the carburetor. By doing so, it ensures the creation of a richer fuel-air mix, especially useful when the engine is cold and fuel doesn't vaporize as effectively. Cold conditions can make fuel stubborn against vaporization. By limiting the air, the choke ensures the engine receives a rich mixture, promoting smoother ignition in these conditions.

The choke helps an engine start on cold days by restricting airflow, which enriches the air-fuel mixture with more fuel to compensate for the reduced evaporation of liquid fuel in cold temperatures. Cold air is denser, allowing for more oxygen, but the challenge lies in the fuel's ability to vaporize for ignition. When the choke is engaged, it creates a vacuum that pushes additional fuel into the combustion chamber, increasing the chances of successful ignition. Once the engine warms up, the choke can be released to restore normal operation and achieve a proper air-fuel ratio for efficient combustion. Overall, the choke is essential for overcoming the difficulties of cold starts, ensuring that the engine can ignite and run smoothly.

Source: https://www.physicsforums.com/thread...d-days.632720/

Re: choke only cold engines?
 

Basically, the cold motor likes a richer mix of fuel/ air ratio. Once warm the combustion is efficient enough to be happy with a leaner mixture. Lean is better for power, fuel consumption, clean burn....until you get too lean then you will get pinging,pre cumbustion, and the racers will start to melt pistons.

Re: choke only cold engines?
 

there is no secret to it. the word "cold" does not designate any particular temperature. January in Minnesota is "cold" at -20F, in Florida "cold" might be 40F.

a "cold" engine is simply one that needs to be choked. but in general a "cold" engine is one at ambient temperature, and a "warm" one at about 160F.

and so, any engine, in general, that has yet to reach about 160F could, repeat COULD, need choking to perform adequately.

with a manual choke, the driver determines how much choke is necessary depending on their experience. automatic chokes, OTOH, are designed to start choking at a given level and reduce that level, eventually to zero, as the engine warms up.

Re: choke only cold engines?
 

Well its that time of the year here winter is like 8 months of it. the only wheels I drive is a 46 super deluxe. We rebuilt the engine 10 yrs ago and never used the choke no matter how cold it gets. By habit I give it 2 pumps and pull throttle a tinch press the start and instant idle. BUT here's the price to pay ! The temp starts rising heater starts heating and it goes from purring like cat to running ragged and now the gas pedal won't budge hard as a rock. Its like some people struggle with vapor lock which I have never ever had but this I have had. I think high vacuum which I have maybe the cause and the cause is the throttle body gets snow white & throttle plates frozen.As the stats start to open I finally can move the gas pedal and it breaks out of it purring (cause I balanced everything = every thing that spins) wonder If anyone suffers with this ! Oh I don't have any wheat pennies in there but have the spacer under the carb the phenolic or whatever its called...

Re: choke only cold engines?
 

Yeah, carburetor icing is a real thing that can happen under certain temp/humidity conditions. Small airplane landing procedure calls for pulling the carb heat lever before going to idle on the throttle; directs some exhaust heat to the carb to prevent carb icing.

I don't think carb icing was common back in the day when these cars were taking people to work every day in very cold climates. Suspect your phenolic spacer is defeating what the Ford engineers designed to prevent this problem.