Choke question

[shed driver]

Back in the 1970's my dad used to say that leaving a car for a prolonged period with the choke out made it easier to start. I've recently picked my classic up from the body shop and it had been stood for well over six weeks. It had been started once or twice in that time to drive in and out of the paint booth. When I went to start it up the choke was out (with the obligatory clothes peg!) and it fired up instantaneously.

Does leaving the choke out do anything?

SD.

[Mumble]

I'm not sure it does, be interesting to find out

[NRG1976]

shed driver said:

Back in the 1970's my dad used to say that leaving a car for a prolonged period with the choke out made it easier to start. I've recently picked my classic up from the body shop and it had been stood for well over six weeks. It had been started once or twice in that time to drive in and out of the paint booth. When I went to start it up the choke was out (with the obligatory clothes peg!) and it fired up instantaneously.

Does leaving the choke out do anything?

SD.

The choke just regulates how much air goes into the carb, hence the only time it influences car start up (as an example) is when the engine is being turned over. So leaving the choke out when the car is sat for a long period does nothing.

[texaxile]

I was given advice back in the day on my manually choke adapted Ford Capri that leaving it open while running too much can "wash the bores".

I have no idea if it is true or not, but all I'll say is that fuel injection did away with such witchcraft.

[Caddyshack]

texaxile said:

I was given advice back in the day on my manually choke adapted Ford Capri that leaving it open while running too much can "wash the bores".

I have no idea if it is true or not, but all I'll say is that fuel injection did away with such witchcraft.

That would make some sense as the choke could be adding much more fuel which could wash the bores.

Leaving the choke out on a non running car would do nothing.

[Sebring440]

Maybe there's a vague theory here.

You stop a warm engine. Then pull the choke out, which closes over the choke flap.

This (almost) seals off the area below the choke flap, so any petrol lying down there does not evaporate. Thus this petrol (may) still be there the next time to come to start from cold?

All bo||ox of course, just pull out the choke, fire it up and drive away.

[Caddyshack]

Sebring440 said:

Maybe there's a vague theory here.

You stop a warm engine. Then pull the choke out, which closes over the choke flap.

This (almost) seals off the area below the choke flap, so any petrol lying down there does not evaporate. Thus this petrol (may) still be there the next time to come to start from cold?

All bo||ox of course, just pull out the choke, fire it up and drive away.

I think that would only work of the choke totally sealed the intake, I think most chokes would still have an opening to atmosphere.

[Sebring440]

Caddyshack said:

I think most chokes would still have an opening to atmosphere.

Of course they do, or else the engine wouldn't run at all.

[mac96]

Caddyshack said:

Sebring440 said:

Maybe there's a vague theory here.

You stop a warm engine. Then pull the choke out, which closes over the choke flap.

This (almost) seals off the area below the choke flap, so any petrol lying down there does not evaporate. Thus this petrol (may) still be there the next time to come to start from cold?

All bo||ox of course, just pull out the choke, fire it up and drive away.

I think that would only work of the choke totally sealed the intake, I think most chokes would still have an opening to atmosphere.

I think that idea had something to do with it though. A related idea that I remember- when I started driving and starting some cars was an art form, some older drivers had the habit when stopping of revving the engine and switching off the ignition while accelerator was still depressed, with the justification that it left unburnt petrol in the cylinders making the next start easier.
I always thought that the unburnt petrol would probably have evaporated, and if it hadn't would cause extra wear on the engine on start up (the washing the bores thing) and never did it myself.

[Caddyshack]

Sebring440 said:

Caddyshack said:

I think most chokes would still have an opening to atmosphere.

Of course they do, or else the engine wouldn't run at all.

My stihl 2 stroke blower and my rc car have chokes that close the inlet totally, they are used to draw the fuel through to a point (I believe), the engine will not run with the choke on.

[Caddyshack]

mac96 said:

Caddyshack said:

Sebring440 said:

Maybe there's a vague theory here.

You stop a warm engine. Then pull the choke out, which closes over the choke flap.

This (almost) seals off the area below the choke flap, so any petrol lying down there does not evaporate. Thus this petrol (may) still be there the next time to come to start from cold?

All bo||ox of course, just pull out the choke, fire it up and drive away.

I think that would only work of the choke totally sealed the intake, I think most chokes would still have an opening to atmosphere.

I think that idea had something to do with it though. A related idea that I remember- when I started driving and starting some cars was an art form, some older drivers had the habit when stopping of revving the engine and switching off the ignition while accelerator was still depressed, with the justification that it left unburnt petrol in the cylinders making the next start easier.
I always thought that the unburnt petrol would probably have evaporated, and if it hadn't would cause extra wear on the engine on start up (the washing the bores thing) and never did it myself.

Yeah, pretty sure that the engine has enough air within it plus the small gap left in the choke that fuel would evaporate over a few days, it would surely need to be totally sealed to stop it evaporating. Even a pin hole, over any length of time, would do it surely?

[Panamax]

texaxile said:

I was given advice back in the day on my manually choke adapted Ford Capri that leaving it open while running too much can "wash the bores".

I have no idea if it is true or not, but all I'll say is that fuel injection did away with such witchcraft.

That is all correct. A choke enriches the mixture to assist starting. Today that job is done automatically by the fuel injection, which knows the temperature of the engine before you crank. Once the engine is started the objective is to transition towards normal mixture as swiftly as possible to finesse emissions and economy. If you "leave the choke out" you'll be using more fuel than you need.

The corollary of this is that any unburnt fuel will indeed "wash the bores".

Owners of 6-cylinder BMWs from the 1990s may well have experienced "fail to start" due to a flooded engine. If you started a cold car and moved it a few feet and then turned it off (for instance moving the car on your drive to wash it) the fuel injection would run rich and then you turn the car off. Fuel could remain in the cylinders. Next time you try to start the car the fuel injection identified "cold" mode again and added even more fuel, flooding the engine. Too much fuel and not enough air so car failed to start.

At this point, if it was a carburettor car you'd slowly depress the accelerator to the floor before cranking and then crank the engine until it fired. This suppressed the amount of new fuel entering the cylinders and enabled successful starting as the mixture weakened.

Unfortunately this isn't possible with a fuel injected car. Once the BMW engine was flooded any further cranking just made the problem worse and worse. And then all that excess fuel washed the bores so the piston rings didn't seal properly, compression was lost and the car wouldn't start in a million years.

To fix this you had to remove the fuse for the fuel injection and crank the engine to clear unburnt fuel. Then reinsert the fuse and try again.

AA-men of that era used to carry a plug-in fuse with the fuse wire cut and a 2-core cable attached instead. On the other end of the cable was a push button. AA-man could sit in the driver's seat, cranking the engine and using his push button to switch the fuel injection on and off until eventually the engine fired.

[Caddyshack]

My friend came round with a new to him 2003 big bike, it was an earl fuel injection. He was trying to start it doing all sorts of winding of the throttle. I told him that it is fuel injected. Leave the throttle alone and press the starter and let the ecu do what it does best…it fired in to life.

I think many people even did the throttle pumping on carbs but if it didn’t actually have a fuel pumper it was probably doing more harm than good. My sister even used to rev the nuts off her metro when it finally started as if it was a punishment or maybe to keep it running?

[mac96]

Caddyshack said:

My friend came round with a new to him 2003 big bike, it was an earl fuel injection. He was trying to start it doing all sorts of winding of the throttle. I told him that it is fuel injected. Leave the throttle alone and press the starter and let the ecu do what it does best…it fired in to life.

I think many people even did the throttle pumping on carbs but if it didn’t actually have a fuel pumper it was probably doing more harm than good. My sister even used to rev the nuts off her metro when it finally started as if it was a punishment or maybe to keep it running?

You are bringing back ancient memories.. my Metro often wouldn't stay running for the first few minutes after starting from cold even with the choke in appropriate position, unless you kept the revs up. OK if you could drive off and not have to stop at any junctions, otherwise PITA. TBF it behaved better when freshly serviced, but no chance when it was approaching 12000 mile service interval..

[Caddyshack]

mac96 said:

Caddyshack said:

My friend came round with a new to him 2003 big bike, it was an earl fuel injection. He was trying to start it doing all sorts of winding of the throttle. I told him that it is fuel injected. Leave the throttle alone and press the starter and let the ecu do what it does best…it fired in to life.

I think many people even did the throttle pumping on carbs but if it didn’t actually have a fuel pumper it was probably doing more harm than good. My sister even used to rev the nuts off her metro when it finally started as if it was a punishment or maybe to keep it running?

You are bringing back ancient memories.. my Metro often wouldn't stay running for the first few minutes after starting from cold even with the choke in appropriate position, unless you kept the revs up. OK if you could drive off and not have to stop at any junctions, otherwise PITA. TBF it behaved better when freshly serviced, but no chance when it was approaching 12000 mile service interval..

205 gti 1.6 was like that too…it taught me to heel and toe. I believe on the 205 (which was injected) it was an air leak or a dirty something in the injection that let the revs drop too low on tickover.

[Sebring440]

Caddyshack said:

I think many people even did the throttle pumping on carbs but if it didn’t actually have a fuel pumper it was probably doing more harm than good.

In what way could it possibly do "more harm"? If the carb didn't have an accelerator pump, then pumping the pedal wouldn't have any effect at all.

[StescoG66]

My Alfa Sprint runs sounds a bag of spanners when cold. Needs a little bit of choke on first start for 30 seconds or so, then after that push choke in and let it idle roughly takes a few minutes after that to properly settle. Its called character ..........

[Caddyshack]

Sebring440 said:

Caddyshack said:

I think many people even did the throttle pumping on carbs but if it didn’t actually have a fuel pumper it was probably doing more harm than good.

In what way could it possibly do "more harm"? If the carb didn't have an accelerator pump, then pumping the pedal wouldn't have any effect at all.

If you are cranking the engine and giving it full throttle then closed throttle there is still fuel in the carb float that is being drawn in and the fuel pump is still delivering fuel. You would possibly flood the engine. I guess you meant with no engine cranking, which would do nothing. I meant people trying to start a car who kept pumping the throttle.

[paintman]

Panamax said:

That is all correct. A choke enriches the mixture to assist starting. Today that job is done automatically by the fuel injection, which knows the temperature of the engine before you crank. Once the engine is started the objective is to transition towards normal mixture as swiftly as possible to finesse emissions and economy. If you "leave the choke out" you'll be using more fuel than you need.

The corollary of this is that any unburnt fuel will indeed "wash the bores".

Owners of 6-cylinder BMWs from the 1990s may well have experienced "fail to start" due to a flooded engine. If you started a cold car and moved it a few feet and then turned it off (for instance moving the car on your drive to wash it) the fuel injection would run rich and then you turn the car off. Fuel could remain in the cylinders. Next time you try to start the car the fuel injection identified "cold" mode again and added even more fuel, flooding the engine. Too much fuel and not enough air so car failed to start.

At this point, if it was a carburettor car you'd slowly depress the accelerator to the floor before cranking and then crank the engine until it fired. This suppressed the amount of new fuel entering the cylinders and enabled successful starting as the mixture weakened.

Unfortunately this isn't possible with a fuel injected car. Once the BMW engine was flooded any further cranking just made the problem worse and worse. And then all that excess fuel washed the bores so the piston rings didn't seal properly, compression was lost and the car wouldn't start in a million years.

To fix this you had to remove the fuse for the fuel injection and crank the engine to clear unburnt fuel. Then reinsert the fuse and try again.

AA-men of that era used to carry a plug-in fuse with the fuse wire cut and a 2-core cable attached instead. On the other end of the cable was a push button. AA-man could sit in the driver's seat, cranking the engine and using his push button to switch the fuel injection on and off until eventually the engine fired.

One of the V engined petrol jags did the same. Can't remember the model but it was in the noughties.
One side was easy to get at to remove & dry the plugs, the other wasn't.

I was told - & that was what happened with a customer of mine - that the usual AA fix at the time was a full lift to a dealer. He said that the AA chap who came to his house spent over an hour trying to get it to start before giving up & arranging recovery.

[ferret50]

I was once investigating why my wife's MG1300 was using more petrol than usual. I discovered that she pulled the choke out and hung her handbag on it.....was quite miffed when I told her to put her bloody bag on the seat!