Auto choke releasing too early

[Abandoned_Trolley]

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference. I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a thing
called an "AED" or Automatic Enrichment Device.

It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.

If your car is fitted with anything like this then messing around with
the carbs is a dead end.

However, I have only ever heard of them shutting off too late rather
than too early.

Without further information any speculation is a bit pointless though

[Roger Mills]

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a thing
called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

[Roger Mills]

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

This document may help:
https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter

It describes how the auto choke works on several different varieties of
SU carburettor.

[Cursitor Doom]

On Sun, 23 Jan 2022 22:01:17 +0000, Roger Mills

Post by Roger Mills

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter
It describes how the auto choke works on several different varieties of
SU carburettor.

Thanks, Roger. In the mean time, I've posted all I have on the subject
from the workshop manual here:

https://disk.yandex.com/d/bMitJ0e4YyvT6g

But I very much doubt it will help!

[Peter Hill]

Post by Cursitor Doom
On Sun, 23 Jan 2022 22:01:17 +0000, Roger Mills

Post by Roger Mills

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter
It describes how the auto choke works on several different varieties of
SU carburettor.

Thanks, Roger. In the mean time, I've posted all I have on the subject
https://disk.yandex.com/d/bMitJ0e4YyvT6g
But I very much doubt it will help!

OK that isn't the one I had info on.

Junk the whole lot and fit fuel injection.

[Cursitor Doom]

Post by Peter Hill

Post by Cursitor Doom
On Sun, 23 Jan 2022 22:01:17 +0000, Roger Mills

Post by Roger Mills

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter
It describes how the auto choke works on several different varieties of
SU carburettor.

Thanks, Roger. In the mean time, I've posted all I have on the subject
https://disk.yandex.com/d/bMitJ0e4YyvT6g
But I very much doubt it will help!

OK that isn't the one I had info on.
Junk the whole lot and fit fuel injection.

Seems a bit drastic! I'd be quite happy with a manual pull-out choke,
personally. And that would be a lot more do-able.

[Ian Jackson]

Post by Cursitor Doom

Post by Peter Hill

Post by Cursitor Doom
On Sun, 23 Jan 2022 22:01:17 +0000, Roger Mills

Post by Roger Mills

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter
It describes how the auto choke works on several different varieties of
SU carburettor.

Thanks, Roger. In the mean time, I've posted all I have on the subject
https://disk.yandex.com/d/bMitJ0e4YyvT6g
But I very much doubt it will help!

OK that isn't the one I had info on.
Junk the whole lot and fit fuel injection.

Seems a bit drastic! I'd be quite happy with a manual pull-out choke,
personally. And that would be a lot more do-able.

Are the manual choke kits still available? Back in the 80s, I fitted my
Ford Escort with one, as the new-fangled automatic choke was sometimes a
bit 'iffy'. These days I think it would be rather difficult to find a
path through the bulkhead to route the cable, and a place to mount the
knob.

[Dave Plowman (News)]

Post by Ian Jackson

Post by Cursitor Doom
Seems a bit drastic! I'd be quite happy with a manual pull-out choke,
personally. And that would be a lot more do-able.

Are the manual choke kits still available? Back in the 80s, I fitted my
Ford Escort with one, as the new-fangled automatic choke was sometimes a
bit 'iffy'. These days I think it would be rather difficult to find a
path through the bulkhead to route the cable, and a place to mount the
knob.

There was definitely a manual choke conversion kit for V-8 Rovers fitted
SUs and their starting carb I remember fitting one to a pal's P5B.

The Rolls has bigger SUs, though. IIRC 2" rather than the Rover 1 3/4"

Late SUs (HIF) didn't move the main jet like earlier types - they had a
cold start valve on the side. All to allow them to comply with emission
laws.

I'd ask Burlen Fuel systems if cold start bits can be fitted to the 2"
carb. As regards the linkage and knob. you'd be on your own, for such a
low volume car.

The P5B conversion still comes up from time to time on Ebay, etc.

[Peter Hill]

Post by Cursitor Doom
On Sun, 23 Jan 2022 22:01:17 +0000, Roger Mills

Post by Roger Mills

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter
It describes how the auto choke works on several different varieties of
SU carburettor.

Thanks, Roger. In the mean time, I've posted all I have on the subject
https://disk.yandex.com/d/bMitJ0e4YyvT6g
But I very much doubt it will help!

First warm it up with bonnet open and observe the cam and link. If that
is moving too soon it may be the restrictor in the "stove pipe" elbow.
The test is the very last bit in the manual, you won't have the required
flow meter to test it.

Never seen a bi-metal auto choke heated by exhaust gas before. Usually
electrical or coolant. Or they use a water heated wax capsule. But it
does mean 2 less water hoses, 4 fewer leaky hose connections and no
trapped air when filling the cooling system.

[Cursitor Doom]

Post by Peter Hill

Post by Cursitor Doom
On Sun, 23 Jan 2022 22:01:17 +0000, Roger Mills

Post by Roger Mills

Post by Roger Mills

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

It could make a lot of difference.  I have had a few different Jaguars
with SU carbs fitted, and an auto choke facility implemented by a
thing called an "AED" or Automatic Enrichment Device.
It's basically a small electric 3rd carb sitting between the 2 normal
ones, and when the motor is cold a solenoid operates to open it up and
let some extra rich juice in to the inlet manifold. As you may have
guessed, the solenoid is dependent on the temperature sensor.
If your car is fitted with anything like this then messing around with
the carbs is a dead end.
However, I have only ever heard of them shutting off too late rather
than too early.
Without further information any speculation is a bit pointless though

If it is that sort of device, a short-term fix may be to wire a switch
in parallel with the temperature sensor. That would, in effect, convert
it to a manual choke - but only in the on/off sense rather than the
progressive effect which you got in the old days with cable operated chokes.

https://sucarb.co.uk/technical-auxiliary-enrichment-carburetter
It describes how the auto choke works on several different varieties of
SU carburettor.

Thanks, Roger. In the mean time, I've posted all I have on the subject
https://disk.yandex.com/d/bMitJ0e4YyvT6g
But I very much doubt it will help!

First warm it up with bonnet open and observe the cam and link. If that
is moving too soon it may be the restrictor in the "stove pipe" elbow.
The test is the very last bit in the manual, you won't have the required
flow meter to test it.
Never seen a bi-metal auto choke heated by exhaust gas before. Usually
electrical or coolant. Or they use a water heated wax capsule. But it
does mean 2 less water hoses, 4 fewer leaky hose connections and no
trapped air when filling the cooling system.

Thanks for that, Peter. I might end up taping a thermistor to a
coolant hose to bypass the bi-metal strip in that case - if I can't
remedy the fault with the existing set-up, I mean.

[Tim+]

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

How does the choke normally work? Does it have a heating element?

Just wondering if a voltage regulator might have gone awry and it’s
receiving a full 12V rather than a regulated down 9V say? (All pure
supposition but just trying to work out why it should be opening too fast).

Tim

[Cursitor Doom]

Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

[Abandoned_Trolley]

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

[Cursitor Doom]

On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

[Peter Hill]

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

The mixture screw is connected to a bi-metal strip which alters the
mixture for the choke. It should never require turning by more than a
quarter of a turn in or out. If you try to richen the mixture by
screwing it too far in, you will bend the bi-metal strip which will
weaken the mixture. (and once bent you will never be able to set it
correctly)

[Fredxx]

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

Hardly. Some SU models had their automatic choke adjusted by their ECU.
Some had a bimetal spring.

Why be so awkward to someone who wants to help you?

[Cursitor Doom]

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

Hardly. Some SU models had their automatic choke adjusted by their ECU.
Some had a bimetal spring.
Why be so awkward to someone who wants to help you?

Because I don't want the thread to get de-railed (as will become
apparent in due course no doubt.) I wanted to keep it general,
otherwise some people who might otherwise have chipped in their
hunches will think, "oh that's too exotic for me I wouldn't know
nuthink about that."

[Dave Plowman (News)]

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

Hardly. Some SU models had their automatic choke adjusted by their ECU.
Some had a bimetal spring.
Why be so awkward to someone who wants to help you?

It's Doom. Very secretive about everything. Everyone is out to get him.

Thinking on the Jags I've had. Carb ones had the SU starting carb -AED.
They went injection after that.

Rover used the same unit. Either the Jag factory manual had full overhaul
details or the Rover one. Can't remember - but the other said just fit a
new one.

If I remember the AED from many years ago, it was a solenoid controlled by
a thermostat. Bodge was to add a switch, bypassing the thermostat control.

IIRC, Burlen have re-manufactured them, using original tooling. Won't be
cheap, though.

[Dave Plowman (News)]

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

[Cursitor Doom]

On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

[Fredxx]

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

[Roger Mills]

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

[Fredxx]

Post by Roger Mills

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

I spotted that after my post. It seems there is a solenoid and a
standard bimetallic spring with a cam to set the idle speed.

The SU doesn't have a separate enrichment system to go wrong [1], so
this suggests:
1) The bi-metal coil isn't as effective as it was. It has relaxed so
relative positions has moved to indicate a hotter than actual temperature.
2) The fast idle cam is maladjusted
3) Some other effect that reduces engine efficiency, such as incorrect
ignition or camshaft timing.

All these things could require additional throttle. However as the
condition occurs after 30 seconds (assuming no over-enrichment to cause
revs to drop through chugging/missing) it does look like (1).

[1] I recall a Ford VV carb that over-enriched during the warm-up period
due to a damaged O-ring. Resulting in some chugging.

It would have been so much easier to have posted the type of carb. I
thought ones of this type were fitted to Rollers.

A crappy manual can be found here:

https://manualzz.com/doc/13968572/tsd4400-workshop-manual--rolls-royce-a-chapter-k
Not the similarity with the pic supplied by CD!

Why was CD so worried we might find out what he drives?

[Cursitor Doom]

Post by Fredxx

Post by Roger Mills

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

I spotted that after my post. It seems there is a solenoid and a
standard bimetallic spring with a cam to set the idle speed.
The SU doesn't have a separate enrichment system to go wrong [1], so
1) The bi-metal coil isn't as effective as it was. It has relaxed so
relative positions has moved to indicate a hotter than actual temperature.
2) The fast idle cam is maladjusted
3) Some other effect that reduces engine efficiency, such as incorrect
ignition or camshaft timing.
All these things could require additional throttle. However as the
condition occurs after 30 seconds (assuming no over-enrichment to cause
revs to drop through chugging/missing) it does look like (1).
[1] I recall a Ford VV carb that over-enriched during the warm-up period
due to a damaged O-ring. Resulting in some chugging.
It would have been so much easier to have posted the type of carb. I
thought ones of this type were fitted to Rollers.
https://manualzz.com/doc/13968572/tsd4400-workshop-manual--rolls-royce-a-chapter-k
Not the similarity with the pic supplied by CD!
Why was CD so worried we might find out what he drives?

I don't just drive one car. And that manual's not much help as it
doesn't cover normally aspirated engines by the look of it.

[Fredxx]

Post by Cursitor Doom

Post by Fredxx

Post by Roger Mills

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

I spotted that after my post. It seems there is a solenoid and a
standard bimetallic spring with a cam to set the idle speed.
The SU doesn't have a separate enrichment system to go wrong [1], so
1) The bi-metal coil isn't as effective as it was. It has relaxed so
relative positions has moved to indicate a hotter than actual temperature.
2) The fast idle cam is maladjusted
3) Some other effect that reduces engine efficiency, such as incorrect
ignition or camshaft timing.
All these things could require additional throttle. However as the
condition occurs after 30 seconds (assuming no over-enrichment to cause
revs to drop through chugging/missing) it does look like (1).
[1] I recall a Ford VV carb that over-enriched during the warm-up period
due to a damaged O-ring. Resulting in some chugging.
It would have been so much easier to have posted the type of carb. I
thought ones of this type were fitted to Rollers.
https://manualzz.com/doc/13968572/tsd4400-workshop-manual--rolls-royce-a-chapter-k
Not the similarity with the pic supplied by CD!
Why was CD so worried we might find out what he drives?

I don't just drive one car. And that manual's not much help as it
doesn't cover normally aspirated engines by the look of it.

Yet has identical photos in your link. Are you suggesting your photos
weren't much help either?

Did you sort out the issue?

[Cursitor Doom]

Post by Fredxx

Post by Cursitor Doom

Post by Fredxx

Post by Roger Mills

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

I spotted that after my post. It seems there is a solenoid and a
standard bimetallic spring with a cam to set the idle speed.
The SU doesn't have a separate enrichment system to go wrong [1], so
1) The bi-metal coil isn't as effective as it was. It has relaxed so
relative positions has moved to indicate a hotter than actual temperature.
2) The fast idle cam is maladjusted
3) Some other effect that reduces engine efficiency, such as incorrect
ignition or camshaft timing.
All these things could require additional throttle. However as the
condition occurs after 30 seconds (assuming no over-enrichment to cause
revs to drop through chugging/missing) it does look like (1).
[1] I recall a Ford VV carb that over-enriched during the warm-up period
due to a damaged O-ring. Resulting in some chugging.
It would have been so much easier to have posted the type of carb. I
thought ones of this type were fitted to Rollers.
https://manualzz.com/doc/13968572/tsd4400-workshop-manual--rolls-royce-a-chapter-k
Not the similarity with the pic supplied by CD!
Why was CD so worried we might find out what he drives?

I don't just drive one car. And that manual's not much help as it
doesn't cover normally aspirated engines by the look of it.

Yet has identical photos in your link. Are you suggesting your photos
weren't much help either?

That's what I said earlier up the thread. But some folk here wanted to
see 'em anyway.

Post by Fredxx
Did you sort out the issue?

Haven't had the chance yet.

[Fredxx]

Post by Cursitor Doom

Post by Fredxx

Post by Cursitor Doom

Post by Fredxx

Post by Roger Mills

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort
of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

I spotted that after my post. It seems there is a solenoid and a
standard bimetallic spring with a cam to set the idle speed.
The SU doesn't have a separate enrichment system to go wrong [1], so
1) The bi-metal coil isn't as effective as it was. It has relaxed so
relative positions has moved to indicate a hotter than actual temperature.
2) The fast idle cam is maladjusted
3) Some other effect that reduces engine efficiency, such as incorrect
ignition or camshaft timing.
All these things could require additional throttle. However as the
condition occurs after 30 seconds (assuming no over-enrichment to cause
revs to drop through chugging/missing) it does look like (1).
[1] I recall a Ford VV carb that over-enriched during the warm-up period
due to a damaged O-ring. Resulting in some chugging.
It would have been so much easier to have posted the type of carb. I
thought ones of this type were fitted to Rollers.
https://manualzz.com/doc/13968572/tsd4400-workshop-manual--rolls-royce-a-chapter-k
Not the similarity with the pic supplied by CD!
Why was CD so worried we might find out what he drives?

I don't just drive one car. And that manual's not much help as it
doesn't cover normally aspirated engines by the look of it.

Yet has identical photos in your link. Are you suggesting your photos
weren't much help either?

That's what I said earlier up the thread. But some folk here wanted to
see 'em anyway.

The issue was simply an automatic choke fitted to an SU is a very rare
beast. Even Jags weren't fitted with them.

Post by Cursitor Doom

Post by Fredxx
Did you sort out the issue?

Haven't had the chance yet.

Good luck

[Dave Plowman (News)]

Post by Fredxx
The issue was simply an automatic choke fitted to an SU is a very rare
beast. Even Jags weren't fitted with them.

Eh? Classic XJ engines used from the 50s to 70s - before they went
injection often had the SU extra starting carb system. My 58 3.4 MkI did,
as did my 78 XJ6. Both gave problems and had to be replaced. Rover also
used it too on some P5 and P6. They even made a kit to convert to manual
choke.

Rolls tended to make their own version. Presumably because of the poor
reliability of the SU one. (Although I'm not certain that starting carb
was made by SU)

[Tim+]

Post by Cursitor Doom

Post by Fredxx

Post by Roger Mills

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

Well, he's shown us an extract from a workshop manual which shows two SU
carburettors serving an engine with two banks of cylinders - possibly a
V8. That may narrow it down a bit - but not a lot!

I spotted that after my post. It seems there is a solenoid and a
standard bimetallic spring with a cam to set the idle speed.
The SU doesn't have a separate enrichment system to go wrong [1], so
1) The bi-metal coil isn't as effective as it was. It has relaxed so
relative positions has moved to indicate a hotter than actual temperature.
2) The fast idle cam is maladjusted
3) Some other effect that reduces engine efficiency, such as incorrect
ignition or camshaft timing.
All these things could require additional throttle. However as the
condition occurs after 30 seconds (assuming no over-enrichment to cause
revs to drop through chugging/missing) it does look like (1).
[1] I recall a Ford VV carb that over-enriched during the warm-up period
due to a damaged O-ring. Resulting in some chugging.
It would have been so much easier to have posted the type of carb. I
thought ones of this type were fitted to Rollers.
https://manualzz.com/doc/13968572/tsd4400-workshop-manual--rolls-royce-a-chapter-k
Not the similarity with the pic supplied by CD!
Why was CD so worried we might find out what he drives?

I don't just drive one car. And that manual's not much help as it
doesn't cover normally aspirated engines by the look of it.

Eh? See section K5-13.

Tim

[Nick Finnigan]

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

We'll find out about the engine when an extract is shown from a 1990
workshop manual for a TSD4400, section K - Fuel system.

[Cursitor Doom]

Post by Nick Finnigan

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

We'll find out about the engine when an extract is shown from a 1990
workshop manual for a TSD4400, section K - Fuel system.

Oh - I almost forgot to say. It's a 1984 Bentley Mulsanne (non-turbo).
Any the wiser now? No? Thought not!

[Peter Hill]

Post by Cursitor Doom

Post by Nick Finnigan

Post by Fredxx

Post by Cursitor Doom
On Mon, 24 Jan 2022 15:27:24 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
On Mon, 24 Jan 2022 09:12:26 +0000, Abandoned_Trolley

Post by Abandoned_Trolley

Post by Cursitor Doom
Thanks for the replies, guys.
There's not much I can do other than post a few pages from the
workshop manual, as the way this works is far from simple. I mean, the
mixture is enriched largely by a butterfly valve in the main air
intake - that much is simple - but how that valve is controlled  is
quite complicated. I'll try to put up the relevant pages in the
morning if time permits, but I'm not sure they'll help much!

Yeah, why not - obviously the make and model of car is some sort of secret.

Completely irrelevant.

It is very relevant.

Nope. Counter-productive as will become clear in due course....

When do you think we'll find out? When is due course?

We'll find out about the engine when an extract is shown from a 1990
workshop manual for a TSD4400, section K - Fuel system.

Oh - I almost forgot to say. It's a 1984 Bentley Mulsanne (non-turbo).
Any the wiser now? No? Thought not!

Development work at Crewe was done using LPG.

[Dave Plowman (News)]

Post by Cursitor Doom
Oh - I almost forgot to say. It's a 1984 Bentley Mulsanne (non-turbo).
Any the wiser now? No? Thought not!

If you have a works workshop manual, they generally give very full
overhaul details. My Bentley one did - and the one I've seen for a Shadow.

[Cursitor Doom]

On Wed, 26 Jan 2022 15:36:28 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
Oh - I almost forgot to say. It's a 1984 Bentley Mulsanne (non-turbo).
Any the wiser now? No? Thought not!

If you have a works workshop manual, they generally give very full
overhaul details. My Bentley one did - and the one I've seen for a Shadow.

The pages I uploaded from the workshop manual are all they have to say
on the subject. They do provide some details on rebuilding/resetting
the mechanism to factory spec, but I was hoping for someone who might
remember from back in the day what actually caused this issue and how
they rectified it. They don't tell you in those manuals what the
typical failure mode of any component is.

[Brian]

Post by Cursitor Doom
On Wed, 26 Jan 2022 15:36:28 +0000 (GMT), "Dave Plowman (News)"

Post by Dave Plowman (News)

Post by Cursitor Doom
Oh - I almost forgot to say. It's a 1984 Bentley Mulsanne (non-turbo).
Any the wiser now? No? Thought not!

If you have a works workshop manual, they generally give very full
overhaul details. My Bentley one did - and the one I've seen for a Shadow.

The pages I uploaded from the workshop manual are all they have to say
on the subject. They do provide some details on rebuilding/resetting
the mechanism to factory spec, but I was hoping for someone who might
remember from back in the day what actually caused this issue and how
they rectified it. They don't tell you in those manuals what the
typical failure mode of any component is.

As I said, Rolls make their own, so you'd do better asking on a Rolls
forum.
With the SU one, the common failure was the thermostat. Many replaced it
with a switch inside the car - since any spare parts likely not easily
available. Manual said to just fit a new or exchange unit.

Remembering back to the early days of automatic chokes, I seem to recall
not all were as reliable / popular as they could have been.

Weren’t kits available to convert to manual chokes? (Not SU carbs of
course.)

We had a couple of cars ( an Escort and a Panda) with a manual choke and
they were fine.

[Dave Plowman (News)]

Post by Brian

With the SU one, the common failure was the thermostat. Many replaced it
with a switch inside the car - since any spare parts likely not easily
available. Manual said to just fit a new or exchange unit.

Remembering back to the early days of automatic chokes, I seem to recall
not all were as reliable / popular as they could have been.
Weren‘t kits available to convert to manual chokes? (Not SU carbs of
course.)

They were for SU too. I fitted one for a pal to his P5B Rover.

Post by Brian
We had a couple of cars ( an Escort and a Panda) with a manual choke and
they were fine.

Until someone unused to such things leaves it fully on.

[Peter Hill]

Post by Dave Plowman (News)

Post by Brian

With the SU one, the common failure was the thermostat. Many replaced it
with a switch inside the car - since any spare parts likely not easily
available. Manual said to just fit a new or exchange unit.

Remembering back to the early days of automatic chokes, I seem to recall
not all were as reliable / popular as they could have been.
Weren‘t kits available to convert to manual chokes? (Not SU carbs of
course.)

They were for SU too. I fitted one for a pal to his P5B Rover.

Post by Brian
We had a couple of cars ( an Escort and a Panda) with a manual choke and
they were fine.

Until someone unused to such things leaves it fully on.

Or hangs a handbag on it.

[Dave Plowman (News)]

Gentlemen,
Does anyone know what the usual cause for an automatic choke coming
off too early is? I find cold starting easy enough and get a nice
smooth idle -but only for the first 30 seconds or so whereupon I can
'feel' (as it were) the choke gradually coming off and the engine
starts to go all lumpy until it warms up properly following me holding
it on fast idle for 5-6 minutes. The engine has SU carbs fitted as
standard if that makes any difference.

Need more info. There are lots of ways to do an auto choke with SU carbs.

Early Rolls used a temperature controlled flap valve in the intake - bit
like a conventional choke. Which also did fast idle. Jaguar and Rover used
a separate starting carb. Rover SD1 a similar idea but called a FASD. (The
SU starting carb didn't have a good reliability record - the FASD much
better. Rover went back to manual choke after the SU one, until fitting
the FASD)

Last versions of the SU had the mixture controlled by an ECU feeding
stepper motors.