Choke - WHY is it needed?

[tim]

Any mechanics around?

I understand basically HOW the choke works with the carby etc, and I know what it does practically, but WHY doesn't an engine run well when it's cold?

I'm thinking either the heat is needed for efficient combustion, or less likely the oil is heavy/thick so there's a lot of inertia inside the engine?

[tim]

* I know I could just go and read it on wikipaedia etc, but it's more fun asking it on here

[Cwidova]

it restricts the air going into the motor therefor making it run richer to heat the engine quicker!!!!engines dont run well when cold due to not being able to burn the fuel very well

[fireyrob]

Any mechanics around?

[Glen]

Robs gonna be out in the garage now looking for the choke lever on his 10

[Bogan]

:P it restricts the air going into the motor therefor making it run richer to heat the engine quicker!!!!engines dont run well when cold due to not being able to vaporise the fuel very well

Fixed.

(Yes I cheated and looked it up on Wikipedia, the source of all truth in the universe)

[mike-s]

there are two types of circuits, chokes, and enricheners. They both do the same thing (that is modifying the fuel/air ratio) but do it from different approaches.

The choke is basically a plate that cuts across the front of the carb, massively restricting the quantity of air that can come in, and increasing the ratio of fuel to air inside the engine as the jetting for the fuel remains the same. The enrichener circuit is basically a secondary series of jetting that provides a secondary source of fuel in order to get the engine started up in a reasonably smooth manner.

The aim of both of these methods is to provide enough additional fuel so that even with the poor combustion achieved with the poorly atomised fuel, it has a hope in hell of firing up enough to run half evenly.
Both of these methods are able to be provided this extra fuel in a linear manner, meaning you can provide as much "extra fuel" as required by the engine to start off smoothly regardless of how warm/cold the engine is. Once it is running reasonably well and the revs start to rise slightly, then you can back off/disengage the choke totally.

[fireyrob]

Robs gonna be out in the garage now looking for the choke lever on his 10

First thing when I get home

[Cwidova]

:P it restricts the air going into the motor therefor making it run richer to heat the engine quicker!!!!engines dont run well when cold due to not being able to vaporise the fuel very well

Fixed.

(Yes I cheated and looked it up on Wikipedia, the source of all truth in the universe)

close enough is good enough.....just leave a rag in the inlet helps with cold starts