How to use a choke

[obi_waynne]

A little trip down nostalgia lane! How many of us remember how to use a choke?

What, when and how much? I think I've only owned one car with a choke in my life and to be completely honest I can't remember how the thing worked exactly?

I seem to remember cold days/first starts = more choke and then push the choke in as the engine warms up?

Do you start with your foot on the accelerator or not?

 

[turbonutter69]

I used to use my foot on the accelerator but it shouldn't really be needed with the choke out fully. I've had quite a few cars with a manual choke but most of them didn't even need it provided services and plugs and such were all in tip top condition.

 

[Miniman]

Haha my dad started telling me all about this last night funnily enough, he said it was only needed in cold days and you just pulled it out before starting the engine. Im guessing each car verys though.

 

[Massive]

not clue about this one :s

 

[HDi fun]

Remember them well.

 

[Chippy657]

whats a choke?

 

[HDi fun]

Petrol engines usually need a richer than standard fuel/air mixture for cold starting. Ie. more fuel than would be required per unit of air when running fully warm.

Modern cars are totally self regulating and the drifer is unaware of the process, apart from a slightly high idle speed when the engine is cold.

A choke, in the really old days of SU and Stromberg carbs, literally choked off the airflow upstream of the throttle butterfly. The increase in vacuum density (strange term, perhaps air rarity would be better) caused more fuel to be drawn from the fuel metering jets within the carburettor body.

THe need for extra fuel is because at low engine temperatures the airborne fuel mist would condense on the intake manifold walls, thus, starving the engine of fuel and causing stalling.

Cars with sequential injection need much less help as the injectors generally deliver fuel to the back of the inlet valves just before the valves open. So the condensation problem is largely removed. But the mixture still is slightly richer than normal at this point. This is achieved without 'choking' the engine now. The ECU simply directs the injectors to deliver slighty more fuel than normal.

A higher idle speed is often still set to encourage swift warm up which means that the car is running optimally very soon after a cold start. This is important to protect lambda sensors and the cat itself.

 

[pgarner]

wifes metro needed a little choke to cold start it, unless it was cold then it needed around 3 notches if i remember.
forgot to push it back in one day ran it for 20miles with the choke half out, think it must have run rather rich as stopped and wouldnt restart for 10 mins.
those were the days eh?
christ i must be older than i thought

 

[HDi fun]

That probably cost a few quid in few as well

 

[steviem]

God my first car had one too, a Fiat Uno! God can't remember when i heard someone talking about a choke,haha!!

They took abit of getting used to but once you use it, then it was no hassle. No way the Fiat would have started though without it on a cold morning though!! lol!! She was a great little car!! :cheesy:

 

[HDi fun]

I had a Fiat 127 many millenia ago and that had an early effort at automatic cold start mangement.

I invloved stamping on the accelerator with your right foot and releasing it again before turning the key. It did actually work quite well although the engine, although running sweetly, was idling at slightly over 2000rpm during the whole cold start process.

This made smooth driving extremely hard.

The worst auto choke I encountered was on my 2.0 litre (single) carb fed Montego.

Anyone remember the dreaded stepper motor which wound the jet body downwards to enrich the mixture?

This was hideous, the engine used to misfire and hesitate dreadfully. I replaced it with a manual conversion kit and peace was restored.

 

[obi_waynne]

I took the auto choke off every car I had and replaced it with a manual one. (Generally vauxhalls though but they ran really rough and really didn't appreciate short journeys with the auto choke.)

 

[stamford]

My god I have had so many cars with a manual choke. Not all behaved as they should, the last one being the Mini 25 I had 2 years ago!

I suppose the question to ask is-what was your first fuel injection engined car?

A tough one to remember that far back! I think mine was a Vauxhall Carlton 2.2CDi on a B plate. I never had any classics like the Triumph Pi etc, most of classics were of the carb and twin carb variety.

 

[Chris Green]

IIRC I had three cars with manual chokes - the 1st, a Vitesse. As you pulled out the choke, you could feel the accelerator being pulled away from your foot, which I guess is how the revs were raised. The 2nd, a Midget has twin SUs, where the extra fuelling came from lowering the needle valve seats inside the carbs, so that more petrol came in for less vacuum/air flow (I think). the 3rd was a Mini 1000. Can't remember much about that - think it was another SU.

Even my 1st fuel-injected car, a Golf GTi had easy-to-understand cold starting. A fifth injector cut in when the engine was cold, enriching the mixture by 25%. When an engine jacket heat sensor said so, a solenoid turned it off.