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Won't idle..... #553257
11/01/19 04:43 PM
11/01/19 04:43 PM
Joined: Nov 2018
Posts: 529
Northants, UK
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TBM  Offline OP
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Northants, UK
Now I seem to have a solution to the poor starting, I've got another interesting problem.

On the last three occasions, after I filled the petrol tank (I usually go almost 'brimful') she refuses ti idle. Starts fine, but when I get to a roundabout/junction/trafficlight etc the revs drop and then she stalls.

Starts again fine, and runs OK until the next junction etc. This happens for about 20 miles, and then she cures herself.

Initially I was thinking that tank debris was being stirred up and blocking the idle jet, but the problem is far too uniform and self rectifying for that.

My next thought is a slightly blocked breather vent in the fuel cap. My thinking is that there is much more chance of a vacuum occuring in the tank when she's full, and this affects the fuel flow. At high revx the draw of the fuelpump is strong enough to overcome the vacuum, and when she stalls, it gives the tank a second or two to equalise pressure so she starts OK. Once a couple of litres have been burnt off, the space is too great for a vacuum to occur.

Does that sound plausible? Any other suggestions? I will give the fuel cap a blow through with the airline, although am tempted to buy a lockable one....


1972 4/4 4 seater
Too many ratty motorbikes
Re: Won't idle..... [Re: TBM] #553291
11/01/19 06:57 PM
11/01/19 06:57 PM
Joined: Aug 2010
Posts: 2,430
Costock, South Nottinghamshire...
Paul F Offline
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Paul F  Offline
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Joined: Aug 2010
Posts: 2,430
Costock, South Nottinghamshire...
Does the carburettor have a solenoid operated anti-run-on valve?

Experienced similar symptoms on our 1985 car with a loose connection on this valve - but cannot see why this would be linked to filling the tank as in your case. A zero cost option is to check the wire to the carburettor - if there is one.

Do you get a whoosh of air when you remove the cap? If not, unlikely to be your blocked breather option (stress on unlikely - so still possible).

The self rectifying bit is mystifying.


Paul
Costock, UK
2014 4/4 Rolls Royce Garnet Red
Disco 4
Teddy - 17h1 Irish Draught cross
Re: Won't idle..... [Re: TBM] #553296
11/01/19 07:07 PM
11/01/19 07:07 PM
Joined: Nov 2018
Posts: 529
Northants, UK
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Northants, UK
No, carb is a basic twin choke Weber - nothing electrical on it.

The 'slightly blocked' breather idea came to me on the way home, and by the time I got home, she was back running perfectly.

However, if it was blocked enough to get the 'whoosh' I think I'd struggle to get her running at all - I once had fun with a bike - on the way to a bike rally, she cut out. Took the tank bag off, got my tools out, checked plugs, fuses etc and all seem fine. She'd then start, I'd get 10 miles down the road and same problem. This happened four times until I realised the tankbag was blocking the cap breather......


1972 4/4 4 seater
Too many ratty motorbikes
Re: Won't idle..... [Re: TBM] #553328
11/01/19 10:28 PM
11/01/19 10:28 PM
Joined: Jul 2007
Posts: 22,487
Cheltenham, Glos. UK
Graham, G4FUJ Online content
Salty Sea Dog
Graham, G4FUJ  Online Content
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Posts: 22,487
Cheltenham, Glos. UK
It does sound like a breather problem.


Graham (G4FUJ)

D8921 L44FOR '93 4/4 Giallo Fly 2 seat smile
'90 LR 90 SW
'07 MINI Cooper
Re: Won't idle..... [Re: TBM] #553373
12/01/19 09:30 AM
12/01/19 09:30 AM
Joined: Jul 2007
Posts: 13,681
Suffolk
John V6 Offline
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John V6  Offline
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Posts: 13,681
Suffolk
+1. It does to me too.


JohnV6
2006 Indigo Blue Roadster S1
Re: Won't idle..... [Re: TBM] #553377
12/01/19 09:35 AM
12/01/19 09:35 AM
Joined: Sep 2011
Posts: 11,584
Mandello del Lario, Lake Como,...
Gambalunga Offline
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Gambalunga  Offline
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Posts: 11,584
Mandello del Lario, Lake Como,...
It is not going to be your problem but in general terms it is not recommended to "brim" the tank when you fill it. Most recommend to stop at the first cut of of the bowser.

In the case of cars that are fitted with carbon canisters the overfilling of the fuel tank can cause raw fuel to contaminate the carbon canister. This can cause problems. In theory the fuel should be blocked from entering the canister by a valve but this may not always work or it may jam. The raw fuel in the canister may provide too rich a mixture until it is purged because the canister is normally purged of fumes by a connection to the intake manifold.


Peter

[Linked Image]
Re: Won't idle..... [Re: TBM] #553443
12/01/19 01:48 PM
12/01/19 01:48 PM
Joined: Feb 2016
Posts: 1,834
East Harling, Norfolk UK
Richard Wood Offline
Talk Morgan Enthusiast
Richard Wood  Offline
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Posts: 1,834
East Harling, Norfolk UK
Had this on a small capacity single cylinder bike in freezing conditions. The petrol cap breather hole was blocked by ice.


Richard

2018 Roadster - Red/Magnolia - "Morton"
1967 Land Rover series 2a SWB
1960 Velocette Venom
Re: Won't idle..... [Re: TBM] #553444
12/01/19 02:14 PM
12/01/19 02:14 PM
Joined: Apr 2017
Posts: 792
Staffordshire
I
IvorMog Offline
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IvorMog  Offline
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I

Joined: Apr 2017
Posts: 792
Staffordshire
I might have missed some of your earlier posts and threads so forgive me if you've already covered this.

Have you had the carb rebuilt or at least thoroughly cleaned since you've had the car

There are all sorts of things that could cause those symptoms in the carb such as sticky floats or gummed up jets etc.

At least if the carb has been rebuilt you can rule out carb issues.

Last edited by IvorMog; 12/01/19 02:15 PM.

Bob

1999 4/4 1.8 Zetec
Re: Won't idle..... [Re: TBM] #553447
12/01/19 02:53 PM
12/01/19 02:53 PM
Joined: Nov 2018
Posts: 529
Northants, UK
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TBM  Offline OP
Talk Morgan Regular

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Posts: 529
Northants, UK
Yep, carb was cleaned out by Allon White when it first happened.

The uniformity of the problem and then the 'self repair' points me away from the carb,


1972 4/4 4 seater
Too many ratty motorbikes
Re: Won't idle..... [Re: TBM] #553460
12/01/19 04:14 PM
12/01/19 04:14 PM
Joined: Dec 2017
Posts: 216
Colorado, USA
B
britmog Offline
L - Learner Plates On
britmog  Offline
L - Learner Plates On
B

Joined: Dec 2017
Posts: 216
Colorado, USA
Rule number 1:

Never fill the fuel tank beyond the first shut off of the fuel pump on any vehicle of any age.

Such a common mistake to get an extra half gallon into the tank.


Bruce Marshall
1964 4/4 Series V Comp (Megan)
1994 +8 (Maurice)
2013 M3W (Olga)
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