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Idling puzzle #588763
06/08/19 06:33 PM
06/08/19 06:33 PM
Joined: Nov 2012
Posts: 44
UK
S
SCX358G Offline OP
Just Getting Started
SCX358G  Offline OP
Just Getting Started
S

Joined: Nov 2012
Posts: 44
UK
Can anyone suggest the root cause of the following fault on my 1969 4/4?

This a 1600GT Ford crossflow with a single Weber carb, and a mechanical fuel pump, unleaded head, Shell V power fuel. Standard distributor with electronic points. Manual choke.
Car starts and runs normally initially, for maybe 10 mins. Once thoroughly warmed up though, when the engine returns to idle at say a junction, anything but the most gentle application of the accelerator causes the engine to stall. The more rapidly the accelerator is pressed, the more likely the engine stalls (with a bit of a 'whuff' sound). Gradually applying the accelerator avoids the problem. Above idle, engine response/revs is normal. In fact, on recent hot days, if the car is allowed to coast to a halt, say from 30 mph, in neutral, the engine will stall before the car actually comes to a stop. Engine idles at approx. 900 rpm when warmed up and choke is fully in.

Ignition timing and advance are correct, though engine does seem to pink a little pulling up steep hills in a high gear, on a hot day. The problem goes away in the winter, ie cold days.
Carburettor has been cleaned, and the mechanical fuel pump replaced?

Any suggestions?

Many thanks

Last edited by SCX358G; 06/08/19 07:13 PM.

Dave
Blue 4/4 1969, Green +4 1953
Re: Idling puzzle [Re: SCX358G] #588771
06/08/19 07:17 PM
06/08/19 07:17 PM
Joined: Sep 2011
Posts: 13,241
Mandello del Lario
Gambalunga Offline
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Gambalunga  Offline
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Posts: 13,241
Mandello del Lario
Points a bit to a rich mixture particularly if it is OK in cold weather when the motor will run with a richer mixture, . Is there a little black smoke from the exhaust at times or does it smell a little rich? Float level not correct, worn out needle valve, etc.


Peter

[Linked Image]
Re: Idling puzzle [Re: SCX358G] #588799
06/08/19 09:28 PM
06/08/19 09:28 PM
Joined: Sep 2014
Posts: 908
East Sussex, ENGLAND
andymot Offline
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andymot  Offline
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Joined: Sep 2014
Posts: 908
East Sussex, ENGLAND
I think I'd be looking for an air leak in the carb/induction area. Try spraying WD40 or brake cleaner around - it'll get sucked in if you spray the leak point and it'll alter the revs alerting you to the location.
Also maybe fuel starvation - is fuel getting throu ok? A possible culprit is a rubber hose breaking down internally - that would be worse when hot. I'd be looking at the fuel line in the engine bay area first. Float level could be suspect as suggested also.

I have had some dodgy electronic components before - if you had a condenser I'd be swapping that out to check. Not so easy with the electronic kits but if all else seems ok on the fuel side I'd be suspicious of the little box of tricks hiding in the distributor.

Good luck searching.


2015 Morgan 4/4 (Wolf fettled) previously 2014 M3W
MINI Cooper S and numerous BMC/BL relics.

Re: Idling puzzle [Re: SCX358G] #588806
06/08/19 10:19 PM
06/08/19 10:19 PM
Joined: Dec 2011
Posts: 1,943
Seattle, USA
B
Button Offline
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Button  Offline
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B

Joined: Dec 2011
Posts: 1,943
Seattle, USA
My experience with these Weber Downdraft Carbs is that they are very prone to junk in the carb. There is a tiny screen at the fuel input, check it out. I agree about air leaks. Tighten every nut and bolt and then give it spray. I use WD40 if nothing else is handy. Not sure if in the UK ethanol is a problem. In the U.S. Corn Farmers are making lots of money at the expense of fuel hoses etc.


Button
Re: Idling puzzle [Re: Gambalunga] #588823
07/08/19 06:01 AM
07/08/19 06:01 AM
Joined: Aug 2008
Posts: 2,288
Powick
tmg513 Offline
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tmg513  Offline
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Joined: Aug 2008
Posts: 2,288
Powick
Originally Posted by Gambalunga
Points a bit to a rich mixture particularly if it is OK in cold weather when the motor will run with a richer mixture, . Is there a little black smoke from the exhaust at times or does it smell a little rich? Float level not correct, worn out needle valve, etc.

I'd go along with that, for what they cost probably worth doing anyway.


1972 4/4 2 Seater
Re: Idling puzzle [Re: SCX358G] #588827
07/08/19 06:32 AM
07/08/19 06:32 AM
Joined: Jul 2019
Posts: 977
L
Luddite Offline
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Luddite  Offline
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L

Joined: Jul 2019
Posts: 977
When looking for air leaks I employ a length of rubber tube kinda like a stethoscope, one end to my ear the other following round the joints in the carb(s) and inlet manifolding etc. The tube can also come in handy for balancing twin carbs by listening to the tone of the airflow having one end of the tube held close to the intake of the carb..

Re: Idling puzzle [Re: SCX358G] #588842
07/08/19 08:04 AM
07/08/19 08:04 AM
Joined: May 2017
Posts: 34
Cheshire
D
DonM Offline
Just Getting Started
DonM  Offline
Just Getting Started
D

Joined: May 2017
Posts: 34
Cheshire
Seem to remember Weber’s have an extra little pump that squirts fuel into the inlet when the accelerator is pressed to stop this happening. Maybe blocked, faulty.

I had a problem with one that had clear silicone sealant in the float chamber that had been used as a gasket. I cleaned the carb numerous times before I found it.


Don

1982 4/4 4 seater
Re: Idling puzzle [Re: SCX358G] #588843
07/08/19 08:09 AM
07/08/19 08:09 AM
Joined: May 2011
Posts: 1,061
Seamill, Ayrshire
M
Max5 Offline
Has a lot to Say!
Max5  Offline
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M

Joined: May 2011
Posts: 1,061
Seamill, Ayrshire
Sounds like a blockage in the pump jet. With the air cleaner removed check if, when you snap the throttle open manually there is a squirt of petrol from the pump jet. You could also check the integrity of the vacuum advance and retard hose as these can perish and cause a leak.

Re: Idling puzzle [Re: Max5] #588844
07/08/19 08:27 AM
07/08/19 08:27 AM
Joined: Sep 2011
Posts: 13,241
Mandello del Lario
Gambalunga Offline
Member of the Inner Circle
Gambalunga  Offline
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Joined: Sep 2011
Posts: 13,241
Mandello del Lario
Originally Posted by DonM
Seem to remember Weber’s have an extra little pump that squirts fuel into the inlet when the accelerator is pressed to stop this happening. Maybe blocked, faulty.


Originally Posted by Max5
Sounds like a blockage in the pump jet. With the air cleaner removed check if, when you snap the throttle open manually there is a squirt of petrol from the pump jet. You could also check the integrity of the vacuum advance and retard hose as these can perish and cause a leak.

I had forgotten about the throttle pump. Yes I would agree that that could be a cause.

Though I think if that was the case it would still happen in cold weather.


Peter

[Linked Image]
Re: Idling puzzle [Re: SCX358G] #595764
19/09/19 11:19 AM
19/09/19 11:19 AM
Joined: Nov 2017
Posts: 49
M
MOR404 Offline
Just Getting Started
MOR404  Offline
Just Getting Started
M

Joined: Nov 2017
Posts: 49
I almost have the same problem. At times when I go to neutral to stop at an intersection the engine just stops. My mechanic has cleaned the jets on the sides of the Webber carbs on my ford Kent 1600 engine but although in garage the idling was ok when I went on a trial it stalled a couple of times when changing to neutral. The engine was running ok up to yesterday . Although it is not the solution I have also increased the idling revs to 1200 but problem still persists. Any other suggestions besides the above thread.

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