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As user Steve Matthews pointed out on my last question Car interior rattles on idle The ideal use of a coke is "Use the choke until the car warms up properly. You can reduce the amount of choke gradually until it's fully off and keep the car running smooth."

But this brings up further questions that after an hour of searching I found no info on.

  • What is the optimal use of a choke?
  • What are the cons of using it incorrecly?
  • What consecuences does wrong use of choke have on the long run?
  • How important is it to gradually ease off the choke as the car starts warming up?
  • How important is it to not push the engine too far while choke is engaged?

For reference the car is a 1985 Citroen BX, the choke is manual (maybe autochokes weren't popular in Spain) and the engine is a carb. Sorry I don't have a pic at hand but I'll definetly add one once I'm home!

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    What year is this car? Generally cars after 1965 or so had carburetors with automatic chokes on them. Generally cars after 1985 or so had fuel injection. There are some exceptions of course. But wow, how old is this car? (Make, Model, Year and if are so inclined, a photo would be awesome!)
    – zipzit
    Apr 25, 2016 at 10:04

2 Answers 2

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You should avoid over-use of the choke if possible, as over-fuelling the engine will cause more carbon build up, shortening the life of the plugs and reducing the time before the engine needs a "decoke" to get rid of the build-up. Plus it wastes fuel! Of course, too little is just as bad...

I've always gone for the following, though I don't know if it's optimal:

  • Pull the choke out fully
  • Start the engine
  • Immediately push the choke in until the engine just starts to struggle, then pull it back out a little bit so the engine is happy.
  • Start driving.
  • Gradually push it in, a bit at a time, over the next few minutes - the time needed will depend on the ambient temperature, and how quickly your engine warms up. From a warn start you might be able to push it fully in straight away.

You should be running with just enough choke that the engine is running smoothly.

Don't push the engine too far until it's fully warmed up, regardless of whether you're using the choke or not. If you do a lot of short journeys, make sure to regularly take it for a long journey to get it properly warmed up.

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  • Splendid response but there's one thing I'd like to confirm. Is it OK to start the engine with absolutely no choke when warm?
    – EChan42
    Apr 25, 2016 at 11:00
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    Yes, its okay to start the car without choke when its warm. Basically you want to choke as little as possible.
    – zipzit
    Apr 25, 2016 at 11:09
  • Thanks for the insight! Once the car is moving if I keep it slightly rev'd and don't come to a complete stop I usually disengage the choke completely but I guess this is bad too since then I'm using the choke too little. I'll stick to your explanation @zipzit thank you!
    – EChan42
    Apr 25, 2016 at 11:22
  • Er.. what? The engine should idle smoothly when warm with the choke totally disengaged (i.e. with the choke plate full open at the top of the carburetor), and our foot off the gas pedal. If the engine does not idle smoothly with your foot off the accelerator you need to get that fixed (possibly simple adjustments or a carburetor cleaning and / or carb rebuild) You are definitely going to want a service manual for the adjustment procedure. The only tool you should need is a screwdriver.
    – zipzit
    Apr 25, 2016 at 11:27
  • @zipzit I suspect he means "Once the car is moving, but still cold" - As you say, you shouldn't need the choke at all once it is warm.
    – Nick C ♦
    Apr 25, 2016 at 11:59
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What is the optimal use of a choke?

Knowing how to use it as explained by Nic C

What are the cons of using it incorrecly?

Fouling spark plugs which will cause a misfire even after it warms up.

Gasoline getting in the oil past the piston rings due to being over rich too long and and causing pre-mature engine wear and lower compression due to the rings being washed out from raw unburnt gas.

What consequences does wrong use of choke have on the long run?

Same as last question

How important is it to gradually ease off the choke as the car starts warming up?

Very important

How important is it to not push the engine too far while choke is engaged?

Regardless of the choke it is hard on an engine to put too much load on it when it is cold. When oil is cold it does not flow well and this can cause pre-mature engine wear if you do not let the engine warm up all they way before romping on the gas pedal or pulling a heavy load (trailer).

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