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Richard H
Joined: 03 Apr 2009 Posts: 2148 Location: Lincolnshire, UK
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Posted: Sat Apr 25, 2009 8:36 am Post subject: Austin A35 chugging |
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Well, this is a problem with my A35 restoration project, although up to about 3 weeks ago I was using it everyday. The problem started about December time. When you start it on the choke from cold, the engine chuggs and sounds like a V8! If you sit and rev it for about 7-8 seconds it clears. It seems to be temperature related?
I have changed the plugs, points, rotor arm and condenser but the problem continues. I was reminded of this as I got it out of the garage yesterday and I don't want it to be off the road forever Help! _________________ Richard Hughes |
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Rick Site Admin
Joined: 27 Apr 2005 Posts: 22446 Location: UK
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Richard H
Joined: 03 Apr 2009 Posts: 2148 Location: Lincolnshire, UK
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Posted: Sat Apr 25, 2009 9:40 am Post subject: |
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Thanks for the quick reply Rick,
Its fine after the first few seconds and chugs for longer depending on how cold the engine is. Yes it does smell slightly rich but then its running on choke so I thought that was normal. There is no excessive smoke.
The car has an original type Zenith fitted which has done about 10,000 miles. I haven't touched the mixture control at all, so I might have a fiddle with it.
Thanks again _________________ Richard Hughes |
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Richard H
Joined: 03 Apr 2009 Posts: 2148 Location: Lincolnshire, UK
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Posted: Sat Apr 25, 2009 9:45 am Post subject: |
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Oh and by the way there is no smoke at all (maybe a tiny bit ) and it doesn't smell rich at all - when it's running without choke.
Thanks _________________ Richard Hughes |
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peter scott
Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh
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Posted: Sat Apr 25, 2009 9:54 am Post subject: |
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Rick is correct to suggest that it's just running on too rich a mixture but I suspect that the chugging you describe is just normal behaviour for an A35.
The carburettor is just a simple downdraft with a butterfly valve operated from the choke control. It is unlikely that it is providing a richer mixture than was originally intended. The answer is to start on full choke then push the knob in a bit until it runs smoothly. Don't expect it to be as well controlled as a modern fuel injected car where you are unaware of whether it is starting cold or hot.
The only adjustable mixture control is to regulate the mixture at tick over when the engine is at normal temperature. This should not be used to alter behaviour for cold starting. There may be an adjustment for fast idle.
This doesn't alter the mixture but simply sets the tick over speed a little higher when you pull the choke out. Using part choke should permit you to operate the fast idle without actually enrichening the mixture.
HTH
Peter _________________ http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon
Last edited by peter scott on Sat Apr 25, 2009 10:12 am; edited 2 times in total |
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Richard H
Joined: 03 Apr 2009 Posts: 2148 Location: Lincolnshire, UK
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Posted: Sat Apr 25, 2009 9:58 am Post subject: |
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Thanks Peter, but actually it chugs whichever position the choke is in - if it is pushed in it simply chugs slower, at slower revs. I know it isn't normal for an A35 as I was using it for about six months before it started doing this. I also have another A35 which runs pefectly.
Thanks in anticipation, _________________ Richard Hughes |
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peter scott
Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh
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Posted: Sat Apr 25, 2009 10:03 am Post subject: |
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Hi Rich,
Take the air filter off and look at the choke butterfly when you pull out the choke. I think it should be possible to have part choke to give fast idle without the butterfly closing off much. Also compare with what happens in your other car.
Peter _________________ http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon
Last edited by peter scott on Sat Apr 25, 2009 10:05 am; edited 1 time in total |
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Rick Site Admin
Joined: 27 Apr 2005 Posts: 22446 Location: UK
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Richard H
Joined: 03 Apr 2009 Posts: 2148 Location: Lincolnshire, UK
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Posted: Sat Apr 25, 2009 10:08 am Post subject: |
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Thanks Peter and Rick,
I'll have a look at the carb today and try both your suggestions. Your knowledge really is invaluable to me!
Thanks again _________________ Richard Hughes |
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buzzy bee
Joined: 23 Nov 2007 Posts: 3382 Location: South Cheshire
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Posted: Sat Apr 25, 2009 11:07 am Post subject: |
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Hi
You probably know this but if a jet is blocked air sometimes won't clear it if it is only partially blocked, so you can sometimes carefully clear them with a single wire from a wire brush, if the jet is big enough.
Cheers
Dave |
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Phil - Nottingham
Joined: 01 Jan 2008 Posts: 1252 Location: Nottingham
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Posted: Sat Apr 25, 2009 11:11 am Post subject: |
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It will ruin the jet though - use a nylon bristle from a tooth brush. If that does not work renew the jet if is blocked _________________ Rover P2
Rover P4
Rover P5 & P5B
Land Rover S2 & S3
Morris Mini Traveller Mk2 |
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buzzy bee
Joined: 23 Nov 2007 Posts: 3382 Location: South Cheshire
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Posted: Sat Apr 25, 2009 12:20 pm Post subject: |
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Phil - Nottingham wrote: | It will ruin the jet though - use a nylon bristle from a tooth brush. If that does not work renew the jet if is blocked |
Hi
Hasn't hurt any of the ones I have done.
Also a good way to clean out nozzles.
Be careful and you will be fine, if you are not confident in doing it then use a bristle.
Cheers
Dave |
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peter scott
Joined: 18 Dec 2007 Posts: 7118 Location: Edinburgh
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Posted: Sat Apr 25, 2009 1:13 pm Post subject: |
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Hi Rich,
I think that jet blockage is much more likely to cause a weaker mixture rather than a richer one so I suspect this is not your problem.
One other thing to check is the mechanism of the choke butterfly. Zenith carbs have various methods to reduce mixture strength when you rev the engine. In your case I think it will either be a hole in the butterfly that has a spring loaded plate covering it or it will have a butterfly where the spindle is offset from the centre. In the first case the spring loaded plate opens in response to the increased passage of air when you rev up. In the second type the choke control acts on the butterfly spindle through a spring such that the increased airflow on reving is able to push the larger side and partially open the butterfly valve. Check that with the choke pulled out you are able to easily open the butterfly valve against its spring. It should just open without being sticky.
Peter _________________ http://www.nostalgiatech.co.uk
1939 SS Jaguar 2 1/2 litre saloon |
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