6 replies to this topic

[charlie]

when starting my 91 carb cooper from cold without any choke, enigne difficult to star.

When I try to use the manual choke the engine coughs and splutters and wont rev.

I've been round to smell the exhaust gases as it tries to fire up, and I'm sure it smells too rich.

I have set the mixture using colourtune, its spot on, and getting about 40mpg, idle speed ok and fast idle ok.

My question is thus, is there some sort of autochoke or bimetallic system that makes the mixture richer when cold?

This rich smell totally baffled me, any ideas, PLEASE.

[Rob]

There will be a rich mixture when cold as a choke puts more fuel in when cold. This is normal.

The rest I dont know sorry.

[Jammy]

How much are you pulling the choke out. Usually I pull out fully on a cold morning, then almost immeditately push it back in by a cm or so, let it warm up for a couple of seconds, then push it back in so its only a cm or 2 out, then after 5 minutes of driving its all the way back in.

If you try and drive whilst the choke is fully out the engine won't like all the extra fuel its receiving and so will cough and splutter.

[binge]

Jammy has hit the nail on the head.
On a cold morning, I dont even pull my choke right out. It comes out about 3/4.
Then almost immidiatly I push it back in to the first notch (about 1cm out)

Drive like that until the temp needle is in the normal, then push the choke right in.

The engine will be running rich with the choke out as the choke shuts off Air intake and increases Fule intake (Hence the rich petrol smell)

[Jammy]

The engine will be running rich with the choke out as the choke shuts off Air intake and increases Fule intake (Hence the rich petrol smell)

On carbs, I believe it just enrichs the mixture, and in fact, when you pull the choke out for the first cm or so it simply increases the idle speed to stop it from dying.

[charlie]

I think you misunderstand me.

Even WITHOUT any choke, the exhaust smells rich, when cold.

I set the mixture when the engine was warm.

Therefore I'm asking is there anything inside the carb that automatically enriches the mixture on cold mornings, without me touching the choke at all.

I have never dismantled a carb b4 and i am wondering if theres anything inside that causes the mixture to be richer when cold. not counting the manual choke.

sorry for any confusion. thanks

[Jammy]

Not on a carb engine.

In fact on a cold morning the mixture should lean off slightly, as the air is colder it is denser, which means you'll be getting more air into the engine and so a leaner mixture..